fluid drive vs coupler

fluid drive and coupler both are nouns.

Word	Noun	Adjective	Verb	Adverb
fluid drive	Yes	No	No	No
coupler	Yes	No	No	No

As nouns, coupler is a hypernym of fluid drive; that is, coupler is a word with a broader meaning than fluid drive:

fluid drive: an automotive power coupling
coupler: a mechanical device that serves to connect the ends of adjacent objects

Other hypernyms of fluid drive include coupling.

fluid drive (noun)	coupler (noun)
an automotive power coupling	a mechanical device that serves to connect the ends of adjacent objects