Is it ensure, insure, or assure?
1650s, euphemism for "underground sewer," from Latin cloaca "public sewer, drain," from cluere "to cleanse," from PIE root *kleue- "to wash, clean" (cf. Greek klyzein "to dash over, wash off, rinse out," klysma "liquid used in a washing;" Lithuanian šluoju "to sweep;" Old English hlutor, Gothic hlutrs, Old High German hlutar, German lauter "pure, clear"). Use in biology, in reference to eliminatory systems of lower animals, is from 1834. Related: Cloacal (1650s); cloacinal (1857).
cloaca clo·a·ca (klō-ā'kə)
In early embryos, the entodermally lined chamber into which the hindgut and allantois empty.
The common cavity into which the intestinal, genital, and urinary tracts open in vertebrates such as fish, reptiles, birds, and some mammals.
An opening in a diseased bone containing a fragment of dead bone.
Plural cloacae (klō-ā'sē')