Definition
知根知底 is a four-character idiom (成语) meaning to know someone thoroughly — literally 'know the roots and know the bottom.' It implies deep familiarity with someone's background, personality, or history, the way an old friend or family member would. You use it about people you've known for a long time, not about acquaintances. The English 'know the inside story' is misleading — it's about knowing a person, not knowing a secret.
f.e.
to know someone thoroughly / to be very familiar with someone's background
Examples
- ，知根知底。Wǒmen shì lǎo péngyou le, hùxiāng zhī.We're old friends; we know each other inside out.
- ，知根知底。Tā zài zhè jiā gōngsī gàn le èrshí nián, duì měi gè yuángōng doū zhī.He's worked at this company for twenty years and knows every employee thoroughly.
- ，知根知底，。Bié zài tā miànqián sāhuǎng, tā zhī, nǐ piàn bù liǎo tā.Don't lie in front of him — he knows you too well, you can't fool him.
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