Meaning

noun good weather with comfortable temperatures

noun acting in a manner that is gentle and mild and even-tempered

noun mercifulness as a consequence of being lenient or tolerant

originFrom Middle English mildenesse, from Old English mildnes, mildness, equivalent to mild + -ness. Cognate with Old High German miltnissa (“compassion, mercy, sympathy, pity”).

Etymology from Wiktionary, CC BY-SA 3.0