The Collaborative International Dictionary of English v.0.48:

Yea \Yea\ (y[=a] or y[=e]; 277), adv. [OE. ye, ya, [yogh]e,
   [yogh]a, AS. ge['a]; akin to OFries. g[=e], i[=e], OS., D.,
   OHG., G., Dan. & Sw. ja, Icel, j[=a], Goth. ja, jai, and
   probably to Gr. "h^ truly, verily. [root]188. Cf. Yes.]
   [1913 Webster]
   1. Yes; ay; a word expressing assent, or an affirmative, or
      an affirmative answer to a question, now superseded by
      yes. See Yes.
      [1913 Webster]

            Let your communication be yea, yea; nay, nay.
                                                  --Matt. v. 37.
      [1913 Webster]

   2. More than this; not only so, but; -- used to mark the
      addition of a more specific or more emphatic clause. Cf.
      Nay, adv., 2.
      [1913 Webster]

            I therein do rejoice, yea, and will rejoice. --Phil.
                                                  i. 18.
      [1913 Webster]

   Note: Yea sometimes introduces a clause, with the sense of
         indeed, verily, truly. "Yea, hath God said, Ye shall
         not eat of every tree of the garden?" --Gen. iii. 1.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Yea \Yea\, n.
   An affirmative vote; one who votes in the affirmative; as, a
   vote by yeas and nays.
   [1913 Webster]

   Note: In the Scriptures, yea is used as a sign of certainty
         or stability. "All the promises of God in him are yea,
         and in him Amen." --2 Cor. i. 20.
         [1913 Webster]

WordNet (r) 3.0 (2006):

yea
    adv 1: not only so, but; "I therein do rejoice, yea, and will
           rejoice" [syn: yea, yeah]
    n 1: an affirmative; "The yeas have it" [ant: nay]

Moby Thesaurus II by Grady Ward, 1.0:

114 Moby Thesaurus words for "yea":
   Australian ballot, Hare system, OK, a fortiori, above all,
   acceptance, additionally, adherence, admiration, affirmative,
   affirmative attitude, affirmativeness, agreed, all right,
   all the more, along, amen, approbation, approval, as well, aye,
   ballot, besides, blessing, canvass, canvassing, casting vote,
   chiefly, countenance, counting heads, cumulative voting,
   deciding vote, division, dominantly, endorsement, enfranchisement,
   especially, esteem, even, ever so, fagot vote, favor,
   favorable vote, first of all, franchise, graveyard vote, hand vote,
   in chief, in the main, indeed, likewise, list system, mainly, more,
   more than ever, moreover, mostly, nay, never so, no, no end, nod,
   nod of assent, nontransferable vote, particularly, peculiarly,
   plebiscite, plebiscitum, plumper, plural vote, poll, polling,
   predominantly, preferential voting, primarily, principally,
   proportional representation, proxy, record vote, referendum,
   representation, respect, right to vote, rising vote, sanction, say,
   seal of approval, secret ballot, show of hands, single vote,
   snap vote, stamp of approval, still more, straw vote, suffrage,
   thumbs-up, too, transferable vote, truly, verily, viva voce, voice,
   voice vote, vote, voting, voting right, write-in, write-in vote,
   yea vote, yea-saying, yeas and nays, yep, yes, yet