滾瓜爛熟

Simplified: 滚瓜烂熟

gǔnguālànshú ㄍㄨㄣˇ ㄍㄨㄚ ㄌㄢˋ ㄕㄨˊ

    • lit. ripe as a melon that rolls from its vine (idiom) fig. to know fluently
    • to know sth inside out
    • to know sth by heart

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Sources