The Collaborative International Dictionary of English v.0.48:

Biscuit \Bis"cuit\, n. [F. biscuit (cf. It. biscotto, Sp.
   bizcocho, Pg. biscouto), fr. L. bis twice + coctus, p. p. of
   coquere to cook, bake. See Cook, and cf. Bisque a kind of
   porcelain.]
   1. A kind of unraised bread, of many varieties, plain, sweet,
      or fancy, formed into flat cakes, and bakes hard; as, ship
      biscuit.
      [1913 Webster]

            According to military practice, the bread or biscuit
            of the Romans was twice prepared in the oven.
                                                  --Gibbon.
      [1913 Webster]

   2. A small loaf or cake of bread, raised and shortened, or
      made light with soda or baking powder. Usually a number
      are baked in the same pan, forming a sheet or card.
      [1913 Webster]

   3. Earthen ware or porcelain which has undergone the first
      baking, before it is subjected to the glazing.
      [1913 Webster]

   4. (Sculp.) A species of white, unglazed porcelain, in which
      vases, figures, and groups are formed in miniature.
      [1913 Webster]

   Meat biscuit, an alimentary preparation consisting of
      matters extracted from meat by boiling, or of meat ground
      fine and combined with flour, so as to form biscuits.
      [1913 Webster]

WordNet (r) 3.0 (2006):

biscuit
    n 1: small round bread leavened with baking-powder or soda
    2: any of various small flat sweet cakes (`biscuit' is the
       British term) [syn: cookie, cooky, biscuit]

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "biscuit":
   Brussels biscuit, Melba toast, adobe, bisque, bone, bowl, brick,
   brownie, cement, ceramic ware, ceramics, china, cookie, cracker,
   crock, crockery, date bar, dust, enamelware, firebrick, fruit bar,
   ginger snap, gingerbread man, glass, graham cracker, hardtack, jug,
   ladyfinger, macaroon, mummy, parchment, pilot biscuit, porcelain,
   pot, pottery, pretzel, refractory, rusk, saltine, sea biscuit,
   ship biscuit, shortbread, sinker, soda cracker, stick,
   sugar cookie, tile, tiling, urn, vase, wafer, zwieback