From Latin 'fervēre' (to boil), from PIE *bʰrew- — passion and brewing share an etymological source in the image of boiling liquid.
Having or showing great warmth or intensity of spirit, feeling, or enthusiasm.
From Old French "fervent" (fervent, burning), from Latin "fervēns," present participle of "fervēre" (to boil, to seethe, to glow), from PIE *bʰrewh₁- (to boil, to brew, to bubble). The PIE root connects heat, fermentation, and emotional intensity across its descendants. Through Latin: "fervor" (heat, passion), "fervid" (ardent), "effervesce" (to bubble out), and "ferment" (from "fermentum," leaven — that which causes bubbling). Through Germanic