universal joint vs coupling

universal joint and coupling both are nouns.

Word	Noun	Adjective	Verb	Adverb
universal joint	Yes	No	No	No
coupling	Yes	No	No	No

As nouns, coupling is a hypernym of universal joint; that is, coupling is a word with a broader meaning than universal joint:

universal joint: coupling that connects two rotating shafts allowing freedom of movement in all directions
coupling: a mechanical device that serves to connect the ends of adjacent objects

Other hypernyms of universal joint include coupler.

universal joint (noun)	coupling (noun)
coupling that connects two rotating shafts allowing freedom of movement in all directions	the act of pairing a male and female for reproductive purposes
	a mechanical device that serves to connect the ends of adjacent objects
	a connection (like a clamp or vise) between two things so they move together