The Collaborative International Dictionary of English v.0.48:

Posy \Po"sy\, n.; pl. Posies. [Contr. fr. poesy.]
   1. A brief poetical sentiment; hence, any brief sentiment,
      motto, or legend; especially, one inscribed on a ring.
      "The posy of a ring." --Shak.
      [1913 Webster]

   2. [Probably so called from the use of flowers as having an
      enigmatical significance. Wedgwood.] A flower; a bouquet;
      a nosegay. "Bridegroom's posies." --Spenser.
      [1913 Webster]

            We make a difference between suffering thistles to
            grow among us, and wearing them for posies. --Swift.
      [1913 Webster]

WordNet (r) 3.0 (2006):

posy
    n 1: an arrangement of flowers that is usually given as a
         present [syn: bouquet, corsage, posy, nosegay]

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "posy":
   TL, album, ana, analects, bale, bindle, bloom, blossom, blow, bolt,
   boughpot, bouquet, boutonniere, budget, bundle, buttonhole,
   chaplet, compliment, corsage, deck, fagot, fardel, fasces, fascine,
   festoon, flattering remark, floret, floriculture, florilegium,
   floscule, flower, flower arrangement, floweret, gardening, garland,
   horticulture, hortorium, lei, miscellany, nosegay, omnibus, pack,
   package, packet, parcel, polite commendation, quiver, roll,
   rouleau, sheaf, spray, trade-last, truss, wildflower, wreath