burn-out (n.)

also burnout, "drug user," by 1972, slang, from the verbal phrase, which is attested from 1590s in the sense "burn until fuel is exhausted;" see burn (v.) + out (adv.). The immediate source is perhaps the use of the phrase in reference to electrical circuits, "fuse or cease to function from overload" (1931). Also compare burnt out "extinct after entire consumption of fuel" (1837). Meaning "mental exhaustion from continuous effort" is from 1975.