early 14c., from fore- + warn. Related: Forewarned; forewarning.
Entries linking to forewarn
fore-
Middle English for-, fore-, from Old English fore-, often for- or foran-, from fore (adv. & prep.), which was used as a prefix in Old English as in other Germanic languages with a sense of "before in time, rank, position," etc., or designating the front part or earliest time.
warn v.
Old English warnian "to give notice of impending danger," also intransitive, "to take heed," from Proto-Germanic *warōnan (source also of Old Norse varna "to admonish," Old High German warnon "to take heed," German warnen "to warn"), from PIE root *wer- (4) "to cover." Related: Warned; warning.