ad vs flier

ad and flier both are nouns.

Word	Noun	Adjective	Verb	Adverb
ad	Yes	No	No	No
flier	Yes	No	No	No

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

ad: a public promotion of some product or service
flier: an advertisement (usually printed on a page or in a leaflet) intended for wide distribution

ad (noun)	flier (noun)
a public promotion of some product or service	an advertisement (usually printed on a page or in a leaflet) intended for wide distribution
	someone who travels by air
	someone who operates an aircraft