terrible vs frightening

terrible is not a noun while frightening is a noun.

Word	Noun	Adjective	Verb	Adverb
terrible	No	Yes	No	No
frightening	Yes	Yes	No	No

As adjectives, terrible and frightening are synonyms defined as:

Other synonyms of terrible include awful, dire, direful, dread, dreaded, dreadful, fearful, fearsome, horrendous, horrific.

terrible (noun)	frightening (noun)
	the act of inspiring with fear

terrible (adjective)	frightening (adjective)
causing fear or dread or terror	causing fear or dread or terror
extreme in degree or extent or amount or impact
intensely or extremely bad or unpleasant in degree or quality
exceptionally bad or displeasing