flypast vs flying

flypast and flying both are nouns.

Word	Noun	Adjective	Verb	Adverb
flypast	Yes	No	No	No
flying	Yes	Yes	No	No

As nouns, flying is a hypernym of flypast; that is, flying is a word with a broader meaning than flypast:

flypast: a flight at a low altitude (usually of military aircraft) over spectators on the ground
flying: an instance of traveling by air

Other hypernyms of flypast include flight.

flypast (noun)	flying (noun)
a flight at a low altitude (usually of military aircraft) over spectators on the ground	an instance of traveling by air

flypast (adjective)	flying (adjective)
	hurried and brief
	moving swiftly