power unit vs W

power unit and W both are nouns.

Word	Noun	Adjective	Verb	Adverb
power unit	Yes	No	No	No
W	Yes	No	No	No

As nouns, W is a hyponym of power unit; that is, W is a word with a more specific, narrower meaning than power unit:

power unit: a measure of electric power
W: a unit of power equal to 1 joule per second; the power dissipated by a current of 1 ampere flowing across a resistance of 1 ohm

Other hyponyms of power unit include abwatt, milliwatt, watt, kilowatt, kW, megawatt, H.P., horsepower, HP, var, volt-ampere, kilovolt-ampere.

power unit (noun)	W (noun)
a measure of electric power	the 23rd letter of the Roman alphabet
	a unit of power equal to 1 joule per second; the power dissipated by a current of 1 ampere flowing across a resistance of 1 ohm
	the cardinal compass point that is at 270 degrees
	a heavy grey-white metallic element; the pure form is used mainly in electrical applications; it is found in several ores including wolframite and scheelite