trout vs sea trout

trout and sea trout both are nouns.

Word	Noun	Adjective	Verb	Adverb
trout	Yes	No	No	No
sea trout	Yes	No	No	No

As nouns, sea trout is a hyponym of trout; that is, sea trout is a word with a more specific, narrower meaning than trout:

Other hyponyms of trout include rainbow trout, salmon trout.

trout (noun)	sea trout (noun)
any of various game and food fishes of cool fresh waters mostly smaller than typical salmons	silvery marine variety of brown trout that migrates to fresh water to spawn
flesh of any of several primarily freshwater game and food fishes	any of several sciaenid fishes of North American coastal waters
	flesh of marine trout that migrate from salt to fresh water