In the 《尔雅》 (Erya, the earliest Chinese dictionary), each season has its own word for 'sky': 春为苍天 (spring = blue heaven), 夏为昊天 (summer = vast heaven), 秋为旻天 (autumn = compassionate heaven), 冬为上天 (winter = high heaven). 旻 is the autumn-specific term, often glossed as 'merciful' because of harvest abundance.
usage
Outside of classical and poetic registers, you'll encounter 旻 mainly in given names (it carries an elegant, cosmic feel) and in the K-pop world via the Korean given-name reading 'Min' (e.g. SHINee's 旼豪 / Minho).
Top 日 — the sun, pictograph of a disc with a central mark. Here it stands for the bright daytime sky overhead, anchoring 旻 in the celestial family with 旭 (sunrise), 昊 (vast sky), 晴 (clear weather).
Bottom 文 — originally a person with patterned chest tattoos, here mainly a phonetic prop: wén → mín through onset shift. A faint cultural overtone too — the autumn sky in classical poetry is the most 'patterned' of the four seasons' heavens, streaked with cloud and migrating birds.
No stroke data for 旻; the glyph shown is your device font, so component strokes can't be highlighted.
