莫逆之交

mònìzhījiāo
  1. intimate friendship
  2. bosom buddies

CEDICT

very close friends (with complete mutual understanding)

Wiktionary

心意相投、至好无嫌的朋友。语本《庄子．大宗师》：「子祀、子舆、子犁、子来……四人相视而笑，莫逆于心，遂相与为友。」《周书．卷二二．柳庆传》：「机弟弘，……与弘农杨素为莫逆之交。」《北史．卷五四．司马子如传》：「膺之既宰相犹子，兼自有名望，所与游集，尽一时名流，与邢子才、王元景等并为莫逆之交。」也作「莫逆交」、「莫逆之友」。

重編國語辭典

Entry Composition

1 莫逆 mònì
  1. very friendly
  2. intimate
2 之 zhī
  1. (possessive particle, literary equivalent of 的 de)
  2. him
  3. her
  4. it
3 交 jiāo
  1. to hand over; to deliver; to pay (money); to turn over
  2. to make friends
  3. (of lines) to intersect
  4. variant of 跤 jiāo

Related entries

金兰之交 jīnlánzhījiāo intimate friendship (idiom)
八拜之交 bābàizhījiāo
  1. sworn brotherhood
  2. intimate friendship