raver (n.)

early 14c., raven, "to show signs of madness or delirium, to rage in speech," from Old French raver, variant of resver "to dream; wander here and there, prowl; behave madly, be crazy," a word of unknown origin (compare reverie). An identical (in form) verb meaning "to wander, stray, rove" dates from late 14c. in Scottish and northern dialect, and is probably from a Scandinavian word (such as Old Norse rafa). Sense of "talk about (something or someone) enthusiastically or immoderately" is recorded by 1704. Related: Raved; raving.