mid-14c., "make (someone) ardent; set (the spirit, etc.) on fire" with a passion or religious virtue, a figurative sense, from Old French enflamer, from Latin inflammare "to set on fire, kindle," figuratively "to rouse, excite," from in- "in" (see in-(2)) + flammare "to flame," from flamma "a flame" (see flame, n.). Literal sense of "to cause to burn" first recorded in English late 14c. Meaning "to heat, make hot, cause inflammation" is from 1520s. Related: Enflamed; enflaming. Also enflame, but since 16c. the spelling with in- has predominated. Related: Inflamed; Inflaming.