fluttering vs flapping

fluttering and flapping both are nouns.

Word	Noun	Adjective	Verb	Adverb
fluttering	Yes	No	No	No
flapping	Yes	No	No	No

As nouns, fluttering and flapping are synonyms defined as:

Other synonyms of fluttering include flap, flutter.

fluttering (noun)	flapping (noun)
the motion made by flapping up and down	the motion made by flapping up and down