grievous vs grave

grievous is not a noun while grave is a noun.

Word	Noun	Adjective	Verb	Adverb
grievous	No	Yes	No	No
grave	Yes	Yes	Yes	No

As adjectives, grievous and grave are synonyms defined as:

Other synonyms of grievous include dangerous, life-threatening, serious, severe.

As adjectives, grievous and grave are synonyms defined as:

grievous and grave: of great gravity or crucial import; requiring serious thought

Other synonyms of grievous include heavy, weighty.

grievous (noun)	grave (noun)
	a place for the burial of a corpse (especially beneath the ground and marked by a tombstone)
	a mark (`) placed above a vowel to indicate pronunciation
	death of a person

grievous (adjective)	grave (adjective)
causing fear or anxiety by threatening great harm	causing fear or anxiety by threatening great harm
shockingly brutal or cruel	of great gravity or crucial import; requiring serious thought
of great gravity or crucial import; requiring serious thought	dignified and somber in manner or character and committed to keeping promises
causing or marked by grief or anguish

grievous (verb)	grave (verb)
	carve, cut, or etch into a material or surface
	shape (a material like stone or wood) by whittling away at it