知根知底

zhīgēnzhīdǐ

to know intimately

Wiktionary

Entry Composition

=1 知 zhī
  1. to know
  2. to be aware
=1 知 zhì
  1. (obsolete on its own in Standard Chinese) Original form of 智 (zhì, “knowing, wisdom, intelligence”).
  2. Original form of 智 (zhì, “knowing, wisdom, intelligence”).
2 根 gēn
  1. root
  2. basis
  3. classifier for long slender objects, e.g. cigarettes, guitar strings
  4. radical (chemistry)

classifier: 條
3 知底 zhīdǐ to know the inside story; to be in the know