1. the common cavity, occurring in early mammalian embryos, into which the intestinal, urinary, and reproductive canals open. The proximity of these functions and the pleasure involved in them are a major factor in Sigmund Freud’s psychosexual theory.

2. in nonmammalian vertebrates, the cavity through which sperm are discharged in the male, and eggs are laid in the female, and through which wastes are eliminated. [Latin, literally: “sewer,” “drain”] —cloacal adj.