water vapor vs vapour

water vapor and vapour both are nouns.

Word	Noun	Adjective	Verb	Adverb
water vapor	Yes	No	No	No
vapour	Yes	No	No	No

As nouns, vapour is a hypernym of water vapor; that is, vapour is a word with a broader meaning than water vapor:

water vapor: water in a vaporous form diffused in the atmosphere but below boiling temperature
vapour: a visible suspension in the air of particles of some substance

Other hypernyms of water vapor include vapor.

water vapor (noun)	vapour (noun)
water in a vaporous form diffused in the atmosphere but below boiling temperature	the process of becoming a vapor
	a visible suspension in the air of particles of some substance