The Collaborative International Dictionary of English v.0.48:

Pollen \Pol"len\, n. [L. pollen fine flour, fine dust; cf. Gr.
   ?]
   1. Fine bran or flour. [Obs.] --Bailey.
      [1913 Webster]

   2. (Bot.) The fecundating dustlike cells of the anthers of
      flowers. See Flower, and Illust. of Filament.
      [1913 Webster]

   Pollen grain (Bot.), a particle or call of pollen.

   Pollen mass, a pollinium. --Gray.

   Pollen sac, a compartment of an anther containing pollen,
      -- usually there are four in each anther.

   Pollen tube, a slender tube which issues from the pollen
      grain on its contact with the stigma, which it penetrates,
      thus conveying, it is supposed, the fecundating matter of
      the grain to the ovule.
      [1913 Webster]

WordNet (r) 3.0 (2006):

pollen
    n 1: the fine spores that contain male gametes and that are
         borne by an anther in a flowering plant

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "pollen":
   androcyte, antheridium, antherozoid, male gamete, milt, protein,
   scum, seed, semen, seminal fluid, sperm, sperm cell, spermagonium,
   spermatic fluid, spermatid, spermatiophore, spermatium,
   spermatocyte, spermatogonium, spermatophore, spermatozoa,
   spermatozoid, spermatozoon