sights vs gun-sight

sights and gun-sight both are nouns.

Word	Noun	Adjective	Verb	Adverb
sights	Yes	No	No	No
gun-sight	Yes	No	No	No

As nouns, gun-sight is a hyponym of sights; that is, gun-sight is a word with a more specific, narrower meaning than sights:

sights: an optical instrument for aiding the eye in aiming, as on a firearm or surveying instrument
gun-sight: a sight used for aiming a gun

Other hyponyms of sights include bombsight, gunsight.

sights (noun)	gun-sight (noun)
an optical instrument for aiding the eye in aiming, as on a firearm or surveying instrument	a sight used for aiming a gun