The Collaborative International Dictionary of English v.0.48:

Affinity \Af*fin"i*ty\, n.; pl. Affinities. [OF. afinit['e],
   F. affinit['e], L. affinites, fr. affinis. See Affined.]
   [1913 Webster]
   1. Relationship by marriage (as between a husband and his
      wife's blood relations, or between a wife and her
      husband's blood relations); -- in contradistinction to
      consanguinity, or relationship by blood; -- followed by
      with, to, or between.
      [1913 Webster]

            Solomon made affinity with Pharaoh.   --1 Kings iii.
                                                  1.
      [1913 Webster]

   2. Kinship generally; close agreement; relation; conformity;
      resemblance; connection; as, the affinity of sounds, of
      colors, or of languages.
      [1913 Webster]

            There is a close affinity between imposture and
            credulity.                            --Sir G. C.
                                                  Lewis.
      [1913 Webster]

   2. Companionship; acquaintance. [Obs.]
      [1913 Webster]

            About forty years past, I began a happy affinity
            with William Cranmer.                 --Burton.
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   4. (Chem.) That attraction which takes place, at an
      insensible distance, between the heterogeneous particles
      of bodies, and unites them to form chemical compounds;
      chemism; chemical or elective affinity or attraction.
      [1913 Webster]

   5. (Nat. Hist.) A relation between species or higher groups
      dependent on resemblance in the whole plan of structure,
      and indicating community of origin.
      [1913 Webster]

   6. (Spiritualism) A superior spiritual relationship or
      attraction held to exist sometimes between persons, esp.
      persons of the opposite sex; also, the man or woman who
      exerts such psychical or spiritual attraction.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Attraction \At*trac"tion\, n. [L. attractio: cf. F. attraction.]
   1. (Physics) An invisible power in a body by which it draws
      anything to itself; the power in nature acting mutually
      between bodies or ultimate particles, tending to draw them
      together, or to produce their cohesion or combination, and
      conversely resisting separation.
      [1913 Webster]

   Note: Attraction is exerted at both sensible and insensible
         distances, and is variously denominated according to
         its qualities or phenomena. Under attraction at
         sensible distances, there are, -- (1.)

   Attraction of gravitation, which acts at all distances
      throughout the universe, with a force proportional
      directly to the product of the masses of the bodies and
      inversely to the square of their distances apart. (2.)

   Magnetic, diamagnetic, and electrical attraction, each
      of which is limited in its sensible range and is polar in
      its action, a property dependent on the quality or
      condition of matter, and not on its quantity. Under
      attraction at insensible distances, there are, -- (1.)

   Adhesive attraction, attraction between surfaces of
      sensible extent, or by the medium of an intervening
      substance. (2.)

   Cohesive attraction, attraction between ultimate particles,
      whether like or unlike, and causing simply an aggregation
      or a union of those particles, as in the absorption of
      gases by charcoal, or of oxygen by spongy platinum, or the
      process of solidification or crystallization. The power in
      adhesive attraction is strictly the same as that of
      cohesion. (3.)

   Capillary attraction, attraction causing a liquid to rise,
      in capillary tubes or interstices, above its level
      outside, as in very small glass tubes, or a sponge, or any
      porous substance, when one end is inserted in the liquid.
      It is a special case of cohesive attraction. (4.)

   Chemical attraction, or

   affinity, that peculiar force which causes elementary
      atoms, or groups of atoms, to unite to form molecules.
      [1913 Webster]

   2. The act or property of attracting; the effect of the power
      or operation of attraction. --Newton.
      [1913 Webster]

   3. The power or act of alluring, drawing to, inviting, or
      engaging; an attractive quality; as, the attraction of
      beauty or eloquence.
      [1913 Webster]

   4. That which attracts; an attractive object or feature.
      [1913 Webster]

   Syn: Allurement; enticement; charm.
        [1913 Webster]

WordNet (r) 3.0 (2006):

affinity
    n 1: (immunology) the attraction between an antigen and an
         antibody
    2: (anthropology) kinship by marriage or adoption; not a blood
       relationship [ant: blood kinship, cognation,
       consanguinity]
    3: (biology) state of relationship between organisms or groups
       of organisms resulting in resemblance in structure or
       structural parts; "in anatomical structure prehistoric man
       shows close affinity with modern humans" [syn: affinity,
       phylogenetic relation]
    4: a close connection marked by community of interests or
       similarity in nature or character; "found a natural affinity
       with the immigrants"; "felt a deep kinship with the other
       students"; "anthropology's kinship with the humanities" [syn:
       affinity, kinship]
    5: the force attracting atoms to each other and binding them
       together in a molecule; "basic dyes have an affinity for wool
       and silk" [syn: affinity, chemical attraction]
    6: inherent resemblance between persons or things
    7: a natural attraction or feeling of kinship; "an affinity for
       politics"; "the mysterious affinity between them"; "James's
       affinity with Sam"

Moby Thesaurus II by Grady Ward, 1.0:

212 Moby Thesaurus words for "affinity":
   a thing for, accord, accordance, addition, adduction, adjunct,
   affairs, affiliation, agape, agreement, alikeness, alliance,
   allurement, amity, analogy, approximation, aptitude, aptness,
   assemblage, assent, association, attractance, attraction,
   attractiveness, attractivity, bag, bent, bias, bond,
   bonds of harmony, brotherly love, capillarity,
   capillary attraction, caritas, cast, cement of friendship,
   centripetal force, charity, chorus, chosen kind, chumminess,
   closeness, coherence, coincidence, combination, communion,
   community, community of interests, comparison, compatibility,
   conatus, concert, concord, concordance, conduciveness, conformance,
   conformation, conformity, congeneracy, congeniality, congruence,
   congruency, congruity, connateness, connaturality, connaturalness,
   connature, connectedness, connection, consistency, consonance,
   consort, contiguity, contrariety, cooperation, correspondence,
   cup of tea, dealings, deduction, delight, diathesis, disjunction,
   disposition, drag, draw, druthers, eagerness, empathy, equivalence,
   esprit, esprit de corps, familiarity, family connection,
   family favor, family likeness, fancy, fascination, favor,
   feeling for, feeling of identity, fellow feeling, fellowship,
   filiation, fondness, frictionlessness, friendliness,
   generic resemblance, good vibes, good vibrations, gravitation,
   gravity, happy family, harmony, homology, identity, inclination,
   inseparableness, intercourse, intersection, intimacy,
   intimate acquaintance, junction, kinship, leaning, liability,
   liaison, like-mindedness, liking, link, linkage, linking, love,
   magnetism, marital affinity, marriage connection,
   marriage relationship, mateyness, mutual affinity,
   mutual attraction, mutuality, nearness, oneness, overlap,
   palliness, parallelism, partiality, particular choice, peace,
   penchant, personal choice, predilection, predisposition,
   preference, prejudice, prepossession, probability, proclivity,
   proneness, propensity, propinquity, proximity, pull, pulling power,
   rapport, rapprochement, readiness, reciprocity, relatedness,
   relation, relations, relationship, resemblance, self-consistency,
   semblance, sensitivity to, sharing, similarity, simile, similitude,
   soft spot, solidarity, special affinity, style, susceptibility,
   symmetry, sympathy, symphony, sync, synchronism, tally, taste,
   team spirit, tendency, thing, tie, tie-in, timing, traction,
   tropism, tug, turn, twist, type, understanding, uniformity, union,
   unison, unisonance, unity, warp, weakness, willingness



Easton's 1897 Bible Dictionary:

Affinity
   relationship by alliance (2 Chr. 18:1) or by marriage (1 Kings
   3:1). Marriages are prohibited within certain degrees of
   affinity, enumerated Lev. 18:6-17. Consanguinity is relationship
   by blood.


Bouvier's Law Dictionary, Revised 6th Ed (1856):

AFFINITY. A connexion formed by marriage, which places the husband in the
same degree of nominal propinquity to the relations of the wife, as that in
which she herself stands towards them, and gives to the wife the same
reciprocal connexion with the relations of the husband. It is used in
contradistinction to consanguinity. (q.v.) It is no real kindred.
     2. Affinity or alliance is very different from kindred. Kindred are
relations. by blood; affinity is the tie which exists between one of the
spouses with the kindred of the other; thus, the relations, of my wife, her
brothers, her sisters, her uncles, are allied to me by affinity, and my
brothers, sisters, &c., are allied in the same way to my wife. But my
brother and the sister of my wife are not allied by the ties of affinity:
This will appear by the following paradigms

          My wife's father             ---|
          |                               |
          |                               |
     -----------------|                   |
     |                |                   |-- are all allied to me.
Ego ----- My Wife     My wife's sister ---|
                |                         |
                My wife's niece        ---|
                My wife's father       ---|
      My Father     |                     |              |My brother
          |         |                     |              |and my wife's
          |         |                     |              |sister are
    |---------------|          |----------|              |not allied
    |               |          |          |              |to each other
My brother          Ego ---- My wife,  My wife's sister  |

     3. A person cannot, by legal succession, receive an inheritance from a
relation by affinity; neither does it extend to the nearest relations of
husband and wife, so as to create a mutual relation between them. The
degrees of affinity are computed in the same way as those of consanguinity.
See Pothier, Traite du Mariage, part 3, ch. 3, art. 2, and see 5 M. R. 296;
Inst. 1, 10, 6; Dig. 38, 10, 4, 3; 1 Phillim. R. 210; S. C. 1 Eng. Eccl. R.
72; article Marriage.