noun
fast descent; speedy fall; plummeting
Often used figuratively for the rapid setting of the autumn sun, likening it to a well-bucket dropping swiftly. Can also describe any sudden, steep fall.
秋の日は釣瓶落としだ。
The autumn sun sets quickly, like a dropping well-bucket.
株価が釣瓶落としに下がった。
Stock prices plummeted.
Standard kanji spelling; literally 'well-bucket dropping', evoking the swift descent of a bucket into a well.
Mixed kanji-kana spelling; 釣瓶 is sometimes written in kana for simplicity.
急降下 is a more technical term for a steep descent (e.g., of an aircraft), while 釣瓶落とし is a vivid, figurative expression often tied to the swift setting of the autumn sun.
From 釣瓶 (つるべ, 'well-bucket') + 落とし (おとし, 'dropping'), referring to the swift motion of a bucket falling into a well. The exact historical origin is uncertain, but the imagery is well-established in classical and modern Japanese.