be (as) thick as thieves
US /bi əz θɪk əz θiːvz/
UK /bi əz θɪk əz θiːvz/
1.
亲密无间, 情同手足
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.
那两个人从小就亲密无间。
•
The new neighbors are already as thick as thieves with the family next door.
新邻居已经和隔壁一家人亲密无间了。