late 14c., prollen, "move about in search of something," of unknown origin, with no known cognates. Spelling with -w- is from 1500s (cf. bowl), but pronounced "prôll" till late 18c. Meaning "go stealthily in search of prey" is first recorded 1580s. Related: Prowled; prowling. The noun, in on the prowl, is attested from 1803.
Actively seeking; abroad and searching, esp for prey (1836+)adverb phrase
Seeking sexual pleasure and conquest; on the make (1940+)