advert vs direct mail

advert and direct mail both are nouns.

Word	Noun	Adjective	Verb	Adverb
advert	Yes	No	Yes	No
direct mail	Yes	No	No	No

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

advert: a public promotion of some product or service
direct mail: advertising sent directly to prospective customers via the mail

advert (noun)	direct mail (noun)
a public promotion of some product or service	advertising sent directly to prospective customers via the mail

advert (verb)	direct mail (verb)
make a more or less disguised reference to
make reference to
give heed (to)