btu b.th.u. • b.t.u. · · · Info · Definitions · Characters · · btu · · Text Latin · · Script 3 · · Length 1 · · Syllables Definitions · · · (noun) a unit of heat equal to the amount of heat required to raise one pound of water one degree Fahrenheit at one atmosphere pressure; equivalent to 251.997 calories. Synonyms: British thermal unit, BTU, B.Th.U.. · · Noun Definition 1 Characters · · b latin small letter b U+0062 t latin small letter t U+0074 u latin small letter u U+0075