gnat vs buffalo gnat

gnat and buffalo gnat both are nouns.

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

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

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

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