varmint vs vermin

varmint and vermin both are nouns.

Word	Noun	Adjective	Verb	Adverb
varmint	Yes	No	No	No
vermin	Yes	No	No	No

As nouns, varmint and vermin are synonyms defined as:

varmint (noun)	vermin (noun)
any usually predatory wild animal considered undesirable; e.g., coyote	any of various small animals or insects that are pests; e.g. cockroaches or rats
an irritating or obnoxious person	an irritating or obnoxious person