gentleness vs mildness

gentleness and mildness both are nouns.

Word	Noun	Adjective	Verb	Adverb
gentleness	Yes	No	No	No
mildness	Yes	No	No	No

As nouns, gentleness and mildness are synonyms defined as:

gentleness and mildness: acting in a manner that is gentle and mild and even-tempered

Other synonyms of gentleness include softness.

gentleness (noun)	mildness (noun)
acting in a manner that is gentle and mild and even-tempered	mercifulness as a consequence of being lenient or tolerant
the property possessed by a slope that is very gradual	acting in a manner that is gentle and mild and even-tempered
	good weather with comfortable temperatures