be (as) thick as thieves

To be very close friends. Anna and Beth are together all the time these days—they're as thick as thieves.

Name	Pronounced	Usage
Varsha	-	Indian, Hindi, Marathi, Gujarati, Tamil
Theokritos	-	Ancient Greek
Doru	-	Romanian
Giuliano	joo-LYAH-no	Italian
Nanda	-	Hinduism, Indian, Kannada, Tamil
Grozdana	-	Bulgarian, Macedonian, Croatian