Etymology
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watt (n.)
unit of electrical power, 1882, in honor of James Watt (1736-1819), Scottish engineer and inventor. The surname is from an old pet form of Walter and also is in Watson.
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kilowatt (n.)
1884, from kilo- + watt. Kilowatt hour is from 1892. Related: Kilowattage.
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megawatt (v.)

unit of measure equivalent to one million watts, 1885, from mega- "one million" + watt.

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ionosphere (n.)
region of the outer atmosphere, 1926, from ion + sphere. Coined by Scottish radar pioneer Robert A. Watson-Watt (1892-1973). So called because it contains many ions.
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B.T.U. 

1889 as an abbreviation of British Thermal Unit (1862), a commercial unit of electrical energy (the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit); the French Thermal Unit is the amount of heat required to raise 1 kilogram of water 1 degree centigrade. Also from 1889 as an abbreviation of Board of Trade Unit, in electicity "1,000 watt hours."

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horsepower (n.)
also horse-power, unit for measurement of the rate at which a motor works, 1805, from horse (n.) + power (n.); established by Watt as the power needed to lift 33,000 pounds one foot in one minute, which actually is about 1.5 times the power of a strong horse. Much abused in 19c. technical writing as "very fallacious," "shockingly unscientific," etc.
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wattle (n.2)
"fleshy appendage below the neck of certain birds," 1510s (extended jocularly to human beings, 1560s), of uncertain origin and of doubtful relationship to wattle (n.1). Related: Wattled.
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wattle (n.1)
"stakes interlaced with twigs and forming the framework of the wall of a building," Old English watol "hurdle," in plural "twigs, thatching, tiles," related to weðel "bandage," from Proto-Germanic *wadlaz, from PIE *au- (3) "to weave" (see weeds). Surviving in wattle-and-daub "building material for huts, etc." (1808).
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