hardening vs tempering

hardening and tempering both are nouns.

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

As nouns, tempering is a hyponym of hardening; that is, tempering is a word with a more specific, narrower meaning than hardening:

hardening: the act of making something harder (firmer or tighter or more compact)
tempering: hardening something by heat treatment

Other hyponyms of hardening include annealing.

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

hardening (adjective)	tempering (adjective)
	moderating by making more temperate