故
ゆえ · yue · JLPT N1 · noun
reason
故 = cause: 事故 (shìgù) is an accident, literally thing + cause, the reason something happened
The same character appears in 缘故 (yuángù, the reason) and 故事 (gùshi, story, originally the cause of events). In Japanese, 故 is read ゆえ in 故に (yue ni), meaning therefore, which is the reason made explicit.
故 — 古 (old) + 攵 (action/strike)
故 combines 古 'old' as the phonetic with 攵, a variant of 攴 meaning to strike or act. Originally it referred to a cause or reason behind an action. From this it extended to mean 'former, old, deceased' and 'therefore, hence' as a connector.