The Collaborative International Dictionary of English v.0.48:

Kilowatt hour \Kil"o*watt` hour\ (Elec.)
   A unit of work or energy equal to that done by one kilowatt
   acting for one hour; -- approximately equal to 1.34
   horse-power hour.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

kilowatt hour
    n 1: a unit of energy equal to the work done by a power of 1000
         watts operating for one hour [syn: kilowatt hour, kW-
         hr, Board of Trade unit, B.T.U.]