astonishingly

As an adverb astonishingly

is in an astonishing manner; so as to surprise or astonish.

As a verb staggering is

.

As an adjective staggering is

incredible, overwhelming, amazing.

As a noun staggering is

the motion of one who staggers.

As adverbs the difference between astonishingly and flabbergastingly

is that astonishingly is in an astonishing manner; so as to surprise or astonish while flabbergastingly is surprisingly, astonishingly or amazingly.