grievous vs flagitious

grievous and flagitious both are adjectives.

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

As adjectives, grievous and flagitious are synonyms defined as:

Other synonyms of grievous include atrocious, monstrous.

grievous (adjective)	flagitious (adjective)
causing fear or anxiety by threatening great harm	shockingly brutal or cruel
shockingly brutal or cruel	extremely wicked, deeply criminal
of great gravity or crucial import; requiring serious thought
causing or marked by grief or anguish