late 14c., from phrase bi cause, introducing a subordinate clause or phrase, "by cause, for the reason that," from by (prep.) + cause (n.). Modeled on French par cause. Originally often followed by that or why. As an adverb, "by reason, on account" (with of), from late 14c. Clipped form cause (sometimes 'cause) is attested in writing by mid-15c.
