c. 1500, of persons; 1660s of devices; agent noun from heat (v.). Baseball slang meaning "fastball" is attested by 1985.
Entries linking to heater
heat v.
Old English hætan "to make hot; to become hot," from Proto-Germanic *haita- (see heat (n.)). Related: Heated (with many variants in Middle English); heating. Bartlett ("Dictionary of Americanisms," 1848) reports that het, as past tense and past participle of heat, is "Often heard in the mouths of illiterate people." Compare Middle Dutch heeten, Dutch heten, German heizen "to heat."