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 rapat, seperti isi dengan kuku

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.
Dua orang itu sudah sangat rapat sejak kecil.
The new neighbors are already as thick as thieves with the family next door.
Jiran baru itu sudah sangat rapat dengan keluarga sebelah.