fishnet vs gill net

fishnet and gill net both are nouns.

Word	Noun	Adjective	Verb	Adverb
fishnet	Yes	No	No	No
gill net	Yes	No	No	No

As nouns, gill net is a hyponym of fishnet; that is, gill net is a word with a more specific, narrower meaning than fishnet:

fishnet: a net that will enclose fish when it is pulled in
gill net: a flat fishnet suspended vertically in the water to entangle fish by their gills

Other hyponyms of fishnet include drift net, landing net, seine, trammel, trammel net, dragnet, trawl, trawl net.

fishnet (noun)	gill net (noun)
a net that will enclose fish when it is pulled in	a flat fishnet suspended vertically in the water to entangle fish by their gills