Several parts combine into one character.

Compound ideograph: 禾 (grain stalks / rice plant — note this is rice ready for harvest, not just any grain) + 火 (fire). Two competing readings: (1) the golden-red color of ripe grain in late summer fields, like flame; (2) the literal practice of burning crop stubble after harvest. Either way: autumn = harvest time. Identical across 繁體 / 新字体 / 简体.

秋 anchors the autumn season in CJK calendars and mid-autumn festivals: 中秋節 / 中秋节 (Mid-Autumn Festival, the second-most-important Chinese holiday after Lunar New Year, celebrated with mooncakes 月餅), 立秋 (the official start of autumn around August 7), 秋分 (autumn equinox).

Mandarin: qiū, level 1st tone. 秋天 (qiūtiān, autumn / fall), 秋季 (qiūjì, autumn season), 中秋 (Zhōngqiū, Mid-Autumn — both the festival and the season), 秋风 (qiūfēng, autumn wind), 春秋 (Chūnqiū, "Spring and Autumn" — also the name of an ancient Chinese era, 770–476 BCE, and a classical text). The compound 春秋 generally means "history" or "the years" in classical contexts.

Japanese: on-reading シュウ (shū) for compounds — 秋分 (shūbun, autumn equinox), 中秋 (chūshū, mid-autumn), 立秋 (risshū, start of autumn), 春夏秋冬 (shunkashūtō, four seasons — the formal compound). Kun-reading あき (aki) is the everyday word — 秋 (aki, autumn), 秋風 (akikaze, autumn wind), 秋祭り (akimatsuri, autumn festival), 秋空 (akizora, autumn sky).

Korean Chuseok (秋夕 — Korean Thanksgiving / mid-autumn harvest festival) is the most important Korean holiday alongside Seollal. Same character, same season. The Korean tradition is family reunion, ancestor honoring, and rice cake (송편).

Memory aid: rice + fire — the fields burning gold at harvest.