buffalo gnat vs gnat

buffalo gnat and gnat both are nouns.

Word	Noun	Adjective	Verb	Adverb
buffalo gnat	Yes	No	No	No
gnat	Yes	No	No	No

As nouns, gnat is a hypernym of buffalo gnat; that is, gnat is a word with a broader meaning than buffalo gnat:

buffalo gnat: small blackish stout-bodied biting fly having aquatic larvae; sucks the blood of birds as well as humans and other mammals
gnat: any of various small biting flies: midges; biting midges; black flies; sand flies

buffalo gnat (noun)	gnat (noun)
small blackish stout-bodied biting fly having aquatic larvae; sucks the blood of birds as well as humans and other mammals	any of various small biting flies: midges; biting midges; black flies; sand flies
	(British usage) mosquito