gravely vs severely

gravely and severely both are adverbs.

Word	Noun	Adjective	Verb	Adverb
gravely	No	No	No	Yes
severely	No	No	No	Yes

As adverbs, gravely and severely are synonyms defined as:

Other synonyms of gravely include badly, seriously.

gravely (adverb)	severely (adverb)
in a grave and sober manner	to a severe or serious degree
to a severe or serious degree	with sternness; in a severe manner
	causing great damage or hardship