serious vs grievous

serious and grievous both are adjectives.

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

As adjectives, serious and grievous are synonyms defined as:

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

serious (adjective)	grievous (adjective)
concerned with work or important matters rather than play or trivialities	causing fear or anxiety by threatening great harm
completely lacking in playfulness	shockingly brutal or cruel
causing fear or anxiety by threatening great harm	of great gravity or crucial import; requiring serious thought
requiring effort or concentration; complex and not easy to answer or solve	causing or marked by grief or anguish
of great consequence
appealing to the mind