be (as) thick as thieves
informalto be very close friends and share secrets, etc.:
I'm sure she tells Ruth everything we say - they're as thick as thieves, those two.
Thesaurus: synonyms and related words
Friendly
- affable
- amiable
- amicable
- amity
- approachable
- closeness
- comrade
- family-friendly
- first name
- forthcoming
- fraternal
- fraternity
- Freemasonry
- matey
- neighbourly
- nice
- nicely
- outgoing
- thaw
- tête-à-tête
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