hardening vs harden

hardening is a noun but harden is not a noun.

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

hardening (noun)	harden (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

hardening (verb)	harden (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