mildness vs gentleness

mildness and gentleness both are nouns.

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

As nouns, mildness and gentleness are synonyms defined as:

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

Other synonyms of mildness include softness.

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