vapor vs phase transition

vapor and phase transition both are nouns.

Word	Noun	Adjective	Verb	Adverb
vapor	Yes	No	No	No
phase transition	Yes	No	No	No

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

vapor: the process of becoming a vapor
phase transition: a change from one state (solid or liquid or gas) to another without a change in chemical composition

Other hypernyms of vapor include phase change, physical change, state change.

vapor (noun)	phase transition (noun)
the process of becoming a vapor	a change from one state (solid or liquid or gas) to another without a change in chemical composition
a visible suspension in the air of particles of some substance