mail vs snail mail

mail and snail mail both are nouns.

Word	Noun	Adjective	Verb	Adverb
mail	Yes	No	Yes	No
snail mail	Yes	No	No	No

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

Other hyponyms of mail include airmail, airpost, RFD, rural free delivery.

mail (noun)	snail mail (noun)
(Middle Ages) flexible armor made of interlinked metal rings	any mail that is physically delivered by the postal service
a conveyance that transports the letters and packages that are conveyed by the postal system
the system whereby messages are transmitted via the post office
the bags of letters and packages that are transported by the postal service
any particular collection of letters or packages that is delivered

mail (verb)	snail mail (verb)
cause to be directed or transmitted to another place
send via the postal service