be (as) thick as thieves

US /bi əz θɪk əz θiːvz/
UK /bi əz θɪk əz θiːvz/
"be (as) thick as thieves" picture
1.

sangat akrab, seperti saudara

to be very close friends and share secrets, often in a way that excludes others

:
Those two have been as thick as thieves since childhood.
Kedua orang itu sudah sangat akrab sejak kecil.
The new neighbors are already as thick as thieves with the family next door.
Tetangga baru itu sudah sangat akrab dengan keluarga sebelah.