Entry 2 senses Webster, 1913 Animalcule · An·i·mal·cule · IPA /ˌænəˈmælˌkjul/ 01 n. A small animal, as a fly, spider, etc. 1. A small animal, as a fly, spider, etc.[Obs.] 2. An animal, invisible, or nearly so, to the naked eye. See Infusoria.(Zool.) See: Infusoria Phrases & compounds Spermatic animalcules — See Spermatozoa.