The Collaborative International Dictionary of English v.0.48:

Legitimate \Le*git"i*mate\ (-m[asl]t), a. [LL. legitimatus, p.
   p. of legitimare to legitimate, fr. L. legitimus legitimate.
   See Legal.]
   1. Accordant with law or with established legal forms and
      requirements; lawful; as, legitimate government;
      legitimate rights; the legitimate succession to the
      throne; a legitimate proceeding of an officer; a
      legitimate heir.
      [1913 Webster]

   2. Lawfully begotten; born in wedlock.
      [1913 Webster]

   3. Authorized; real; genuine; not false, counterfe`t, or
      spurious; as,$legitimate poems of Chaucer; legitimate
      inscriptions.
      [1913 Webster]

   4. Conforming to known principles, or accepted rules; as,
      legitimate reasoning; a legitimate standard, or method; a
      legitimate combination of colors.
      [1913 Webster]

            Tillotson still keeps his place as a legitimate
            English classic.                      --Macaulay.
      [1913 Webster]

   5. Following by logical sequence; reasonable; as, a
      legitimate result; a legitimate inference.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Legitimate \Le*git"i*mate\ (-m[=a]t), v. t. [imp. & p. p.
   Legitimated (-m[=a]`t[e^]d); p. pr. & vb. n. Legitimating
   (-m[=a]`t[i^]ng).]
   To make legitimate, lawful, or valid; esp., to put in the
   position or state of a legitimate person before the law, by
   legal means; as, to legitimate a bastard child.
   [1913 Webster]

         To enact a statute of that which he dares not seem to
         approve, even to legitimate vice.        --Milton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

legitimate
    adj 1: of marriages and offspring; recognized as lawful [ant:
           illegitimate]
    2: based on known statements or events or conditions; "rain was
       a logical expectation, given the time of year" [syn:
       legitimate, logical]
    3: in accordance with recognized or accepted standards or
       principles; "legitimate advertising practices"
    4: authorized, sanctioned by, or in accordance with law; "a
       legitimate government" [syn: lawful, legitimate, licit]
    v 1: make legal; "Marijuana should be legalized" [syn:
         legalize, legalise, decriminalize, decriminalise,
         legitimize, legitimise, legitimate, legitimatize,
         legitimatise] [ant: criminalise, criminalize,
         illegalise, illegalize, outlaw]
    2: show or affirm to be just and legitimate
    3: make (an illegitimate child) legitimate; declare the
       legitimacy of (someone); "They legitimized their natural
       child"

Moby Thesaurus II by Grady Ward, 1.0:

174 Moby Thesaurus words for "legitimate":
   acceptable, actionable, actor-proof, admissible, all-star,
   allowable, applicable, authentic, authoritative, authorize,
   authorized, ballet, balletic, binding, bona fide, by law, candid,
   card-carrying, certify, cinematic, cinematographic, cogent,
   competent, condonable, consistent, constitutional, correct,
   credible, de jure, defensible, dinkum, dispensable, dramatic,
   dramatical, dramaturgic, excusable, exemptible, expiable, fair,
   film, filmic, following the letter, forgivable, genuine, good, ham,
   hammy, histrionic, honest, honest-to-God, inartificial,
   inoffensive, judicial, juridical, just, justiciable, justifiable,
   kosher, lawful, lawmaking, legal, legalize, legislative, legit,
   legitimatize, legitimize, legitimized, licit, lifelike, literal,
   logical, melodramatic, milked, monodramatic, movie, natural,
   naturalistic, operatic, original, overacted, overplayed,
   pardonable, permissible, plausible, proper, pure, rational, real,
   realistic, reasonable, remissible, right, rightful, sanction,
   sanctionable, sanctioned, sane, scenic, self-consistent, sensible,
   simon-pure, simple, sincere, solid, sound, spectacular, stagelike,
   stageworthy, stagy, starstruck, statutory, stellar, sterling,
   substantial, sufficient, sure-enough, theaterlike, theatrical,
   thespian, thrown away, true, true to life, true to nature,
   true to reality, unadulterated, unaffected, unassumed, unassuming,
   uncolored, unconcocted, uncopied, uncounterfeited, underacted,
   underplayed, undisguised, undisguising, undistorted, unexaggerated,
   unfabricated, unfanciful, unfeigned, unfeigning, unfictitious,
   unflattering, unimagined, unimitated, uninvented, unobjectionable,
   unpretended, unpretending, unqualified, unromantic, unsimulated,
   unspecious, unsynthetic, unvarnished, valid, validate,
   vaudevillian, venial, verbal, verbatim, veridical, verisimilar,
   vindicable, warrant, warrantable, weighty, well-argued,
   well-founded, well-grounded, wholesome, within the law,
   word-for-word



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

LEGITIMATE. That which is according to law; as, legitimate children, are
lawful children, born in wedlock, in contradistinction to bastards;
legitimate authority, or lawful power, in opposition to usurpation.