airman vs flier

airman and flier both are nouns.

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

As nouns, flier is a hypernym of airman; that is, flier is a word with a broader meaning than airman:

Other hypernyms of airman include aeronaut, aviator, flyer, adult male, man.

airman (noun)	flier (noun)
a male who operates an aircraft	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