The Collaborative International Dictionary of English v.0.48:

Spermatozoid \Sper`ma*to*zo"id\, n. [Spermatozoon + Gr. e'i^dos
   form.] (Biol.)
   The male germ cell in animals and plants, the essential
   element in fertilization; a microscopic animalcule-like
   particle, usually provided with one or more cilia by which it
   is capable of active motion. In animals, the familiar type is
   that of a small, more or less ovoid head, with a delicate
   threadlike cilium, or tail. Called also spermatozoon. In
   plants the more usual term is antherozoid.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Spermatozoon \Sper`ma*to*zo"on\, n.; pl. Spermatozoa. [NL.,
   fr. Gr. ???, sperm + zo^,on an animal.] (Biol.)
   Same as Spermatozoid.
   [1913 Webster]

WordNet (r) 3.0 (2006):

spermatozoon
    n 1: the male reproductive cell; the male gamete; "a sperm is
         mostly a nucleus surrounded by little other cellular
         material" [syn: sperm, sperm cell, spermatozoon,
         spermatozoan]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "spermatozoon":
   Anlage, androcyte, antheridium, antherozoid, bud, egg, embryo,
   germ, germen, loins, male gamete, milt, nucleus, ovum, pollen,
   protein, rudiment, scum, seed, semen, seminal fluid, sperm,
   sperm cell, spermagonium, spermatic fluid, spermatid,
   spermatiophore, spermatium, spermatocyte, spermatogonium,
   spermatophore, spermatozoa, spermatozoid