mid-14c., from Old French fervent "fervent, ardent" (12c.), from Latin ferventem (nominative fervens) "boiling, hot, glowing," figuratively "violent, impetuous, furious," present participle of fervere "to boil, glow," from PIE root *bhreuə- "to boil, bubble" (see brew, v.). The figurative sense of "impassioned" is first attested c.1400. Related: Fervency; fervently.