- Noun. (biology) An organic body or cell having locomotion, as a spermatic cell or spermatozoid.
- Noun. (zoology) An animal in one of its inferior or early stages of development, as one of the intermediate forms in alternate generation.
- Noun. (zoology) One of the individual animals in a composite group, as of Anthozoa, Hydroidea, and Bryozoa; — sometimes restricted to those individuals in which the mouth and digestive organs are not developed.