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Meaning of British thermal unit

Brit'ish ther'mal u"nit

Pronunciation: [key]
— Physics. Physics.
  1. the amount of heat required to raise the temperature of 1 lb. (0.4 kg) of water 1°F. Abbr.: Btu, BTU, B.t.u., B.T.U., B.th.u.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.