The Collaborative International Dictionary of English v.0.48:

Relationship \Re*la"tion*ship\, n.
   The state of being related by kindred, affinity, or other
   alliance. --Mason.
   [1913 Webster]

WordNet (r) 3.0 (2006):

relationship
    n 1: a relation between people; (`relationship' is often used
         where `relation' would serve, as in `the relationship
         between inflation and unemployment', but the preferred
         usage of `relationship' is for human relations or states of
         relatedness); "the relationship between mothers and their
         children" [syn: relationship, human relationship]
    2: a state of connectedness between people (especially an
       emotional connection); "he didn't want his wife to know of
       the relationship"
    3: a state involving mutual dealings between people or parties
       or countries
    4: (anthropology) relatedness or connection by blood or marriage
       or adoption [syn: kinship, family relationship,
       relationship]

Moby Thesaurus II by Grady Ward, 1.0:

74 Moby Thesaurus words for "relationship":
   accord, addition, adjunct, affairs, affiliation, affinity,
   agnation, alliance, ancestry, approximation, assemblage,
   association, blood, blood relationship, bond, brotherhood,
   brothership, closeness, cognation, combination, common ancestry,
   common descent, connectedness, connection, consanguinity,
   contiguity, contrariety, cousinhood, cousinship, dealings,
   deduction, disjunction, enation, fatherhood, filiation, fraternity,
   homology, intercourse, intimacy, junction, kindred, kinship,
   liaison, link, linkage, linking, maternity, matrilineage,
   matriliny, matrisib, matrocliny, motherhood, mutual attraction,
   nearness, paternity, patrilineage, patriliny, patrisib, patrocliny,
   propinquity, proximity, rapport, relatedness, relation, relations,
   sibship, similarity, sisterhood, sistership, sympathy, tie, tie-in,
   ties of blood, union