The Collaborative International Dictionary of English v.0.48:

Cognate \Cog"nate\, a. [L. cognatus; co- + gnatus, natus, p. p.
   of nasci, anciently gnasci, to be born. See Nation, and cf.
   Connate.]
   1. Allied by blood; kindred by birth; specifically (Law),
      related on the mother's side.
      [1913 Webster]

   2. Of the same or a similar nature; of the same family;
      proceeding from the same stock or root; allied; kindred;
      as, a cognate language.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cognate \Cog"nate\, n.
   1. (Law) One who is related to another on the female side.
      --Wharton.
      [1913 Webster]

   2. One of a number of things allied in origin or nature; as,
      certain letters are cognates.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cognate
    adj 1: related in nature; "connate qualities" [syn: connate,
           cognate]
    2: having the same ancestral language; "cognate languages"
    3: related by blood [syn: akin(p), blood-related, cognate,
       consanguine, consanguineous, consanguineal, kin(p)]
    n 1: one related by blood or origin; especially on sharing an
         ancestor with another [syn: blood relation, blood
         relative, cognate, sib]
    2: a word is cognate with another if both derive from the same
       word in an ancestral language [syn: cognate, cognate
       word]

Moby Thesaurus II by Grady Ward, 1.0:

127 Moby Thesaurus words for "cognate":
   affiliated, affinal, affinitive, agnate, akin, allied, ally,
   alter ego, analogon, analogue, ancestry, associate, avuncular,
   blood, blood relation, blood relative, brother, clansman,
   close copy, close match, closely related, collateral,
   collateral relative, common, companion, complement, congenator,
   congener, congeneric, congenerous, congenial, connate, connatural,
   connected, connections, consanguine, consanguinean, consanguineous,
   conspecific, coordinate, correlate, correlative, correspondent,
   counterpart, derivation, derivative, distaff side,
   distant relation, distantly related, doublet, enate, eponym,
   equivalent, etymon, family, fellow, flesh, flesh and blood, folks,
   foster, general, generic, genetically related, german, germane,
   image, incident, kin, kindred, kindred spirit, kinfolk, kinnery,
   kinsfolk, kinsman, kinsmen, kinswoman, kith and kin, like,
   likeness, mate, matrilateral, matrilineal, matroclinous,
   near duplicate, near relation, next of kin, novercal, obverse,
   of common source, of the blood, parallel, patrilateral,
   patrilineal, patroclinous, pendant, people, picture, posterity,
   primitive, reciprocal, related, related by blood, relations,
   relatives, root, second self, sib, sibling, similitude, simulacrum,
   sister, soul mate, spear kin, spear side, spindle kin,
   spindle side, such, suchlike, sword side, tally, the like of,
   the likes of, tribesman, twin, universal, uterine, uterine kin