frightening vs direful

frightening is a noun but direful is not a noun.

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

As adjectives, frightening and direful are synonyms defined as:

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

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

frightening (adjective)	direful (adjective)
causing fear or dread or terror	causing fear or dread or terror