铁子

鐵子
tiězi
  1. (slang) very close friend
  2. bro

CEDICT

slang

Entry Composition

1 铁 tiě
  1. iron (metal)
  2. arms
  3. weapons
  4. hard
  5. strong
  6. violent
  7. unshakeable
  8. determined
  9. close
  10. tight (slang)
2 子 zi noun suffix, as in 椅子 yǐzi "chair"