Spermatocide: Any agent that is destructive to spermatozoa (that is, kills sperm).
Nonoxynol-9 is the most commonly encountered spermatocide in the United States. (The nonoxynols, technically speaking, are nonionic surfactant [surface active] mixtures that vary in the number of repeating ethoxy groups.) They are much used as detergents, emulsifiers, wetting and defoaming agents, etc. Nonoxynol-9 has 9 repeating ethoxy groups and is the active component of most vaginal foams and creams.