harden vs hardening

harden is not a noun while hardening is a noun.

Word	Noun	Adjective	Verb	Adverb
harden	No	No	Yes	No
hardening	Yes	No	No	No

harden (noun)	hardening (noun)
	the act of making something harder (firmer or tighter or more compact)
	the process of becoming hard or solid by cooling or drying or crystallization
	abnormal hardening or thickening of tissue

harden (verb)	hardening (verb)
become hard or harder
make hard or harder
make healthy
cause to accept or become hardened to; habituate
harden by reheating and cooling in oil