swivel vs coupling

swivel and coupling both are nouns.

Word	Noun	Adjective	Verb	Adverb
swivel	Yes	No	Yes	No
coupling	Yes	No	No	No

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

swivel: a coupling (as in a chain) that has one end that turns on a headed pin
coupling: a mechanical device that serves to connect the ends of adjacent objects

Other hypernyms of swivel include coupler.

swivel (noun)	coupling (noun)
a coupling (as in a chain) that has one end that turns on a headed pin	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

swivel (verb)	coupling (verb)
turn on a pivot