flabbergasted vs dumfounded

flabbergasted and dumfounded both are adjectives.

Word	Noun	Adjective	Verb	Adverb
flabbergasted	No	Yes	No	No
dumfounded	No	Yes	No	No

As adjectives, flabbergasted and dumfounded are synonyms defined as:

flabbergasted and dumfounded: as if struck dumb with astonishment and surprise

Other synonyms of flabbergasted include dumbfounded, dumbstricken, dumbstruck, stupefied, thunderstruck.

flabbergasted (adjective)	dumfounded (adjective)
as if struck dumb with astonishment and surprise	as if struck dumb with astonishment and surprise