fearfulness vs fearful

fearfulness is a noun but fearful is not a noun.

Word	Noun	Adjective	Verb	Adverb
fearfulness	Yes	No	No	No
fearful	No	Yes	No	No

fearfulness (noun)	fearful (noun)
the trait of being afraid
an emotion experienced in anticipation of some specific pain or danger (usually accompanied by a desire to flee or fight)

fearfulness (adjective)	fearful (adjective)
	lacking courage; ignobly timid and faint-hearted
	experiencing or showing fear
	causing fear or dread or terror
	extremely distressing
	timid by nature or revealing timidity