early 14c., "to show signs of madness or delirium," from Old French raver, variant of resver "to dream; wander here and there, prowl; behave madly, be crazy," of unknown origin (compare reverie). The identical (in form) verb meaning "to wander, stray, rove" first appeared c. 1300 in Scottish and northern dialect, and is probably from an unrelated Scandinavian word (such as Icelandic rafa). Sense of "talk enthusiastically about" first recorded 1704. Related: Raved; raving.