The Collaborative International Dictionary of English v.0.48:

Semen \Se"men\ (s[=e]"m[e^]n), n.; pl. Semina
   (s[e^]m"[i^]*n[.a]). [L., from the root of serere, satum, to
   sow. See Sow to scatter seed.]
   1. (Bot.) The seed of plants.
      [1913 Webster]

   2. (Physiol.) The seed or fecundating fluid of male animals;
      sperm. It is a white or whitish viscid fluid secreted by
      the testes, characterized by the presence of spermatozoids
      to which it owes its generative power.
      [1913 Webster]

   Semen contra, or Semen cinae or Semen cynae, a strong
      aromatic, bitter drug, imported from Aleppo and Barbary,
      said to consist of the leaves, peduncles, and unexpanded
      flowers of various species of Artemisia; wormseed.
      [1913 Webster]

WordNet (r) 3.0 (2006):

semen
    n 1: the thick white fluid containing spermatozoa that is
         ejaculated by the male genital tract [syn: semen, seed,
         seminal fluid, ejaculate, cum, come]

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "semen":
   androcyte, antheridium, antherozoid, autacoid, bile, chalone,
   digestive secretion, endocrine, gall, gastric juice, hormone,
   intestinal juice, male gamete, milt, mucus, pancreatic juice,
   pollen, prostatic fluid, protein, rheum, salivary secretion, scum,
   seed, seminal fluid, sperm, sperm cell, spermagonium,
   spermatic fluid, spermatid, spermatiophore, spermatium,
   spermatocyte, spermatogonium, spermatophore, spermatozoa,
   spermatozoid, spermatozoon, tears, thyroxin