brown trout vs salmon trout

brown trout and salmon trout both are nouns.

Word	Noun	Adjective	Verb	Adverb
brown trout	Yes	No	No	No
salmon trout	Yes	No	No	No

As nouns, brown trout and salmon trout are synonyms defined as:

brown trout and salmon trout: speckled trout of European rivers; introduced in North America

Other synonyms of brown trout include Salmo trutta.

brown trout (noun)	salmon trout (noun)
speckled trout of European rivers; introduced in North America	large fork-tailed trout of lakes of Canada and the northern United States
	speckled trout of European rivers; introduced in North America
	flesh of marine trout that migrate from salt to fresh water