sights vs gunsight

sights and gunsight both are nouns.

Word	Noun	Adjective	Verb	Adverb
sights	Yes	No	No	No
gunsight	Yes	No	No	No

As nouns, gunsight is a hyponym of sights; that is, gunsight 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
gunsight: a sight used for aiming a gun

Other hyponyms of sights include bombsight, gun-sight.

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