mildness vs leniency

mildness and leniency both are nouns.

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

As nouns, mildness and leniency are synonyms defined as:

mildness and leniency: mercifulness as a consequence of being lenient or tolerant

Other synonyms of mildness include lenience, lenity.

mildness (noun)	leniency (noun)
mercifulness as a consequence of being lenient or tolerant	lightening a penalty or excusing from a chore by judges or parents or teachers
acting in a manner that is gentle and mild and even-tempered	mercifulness as a consequence of being lenient or tolerant
good weather with comfortable temperatures	a disposition to yield to the wishes of someone