thick as thieves
Meaning
Very close friends who spend a lot of time together and often share secrets.
Origin
“Thick” has long meant “close/intimate” (as in “thick with someone”), and “thieves” evokes partners-in-crime who must trust each other and keep secrets. The simile has been used since at least the 19th century.
Notes
Common, informal way to say two people are extremely close and often share secrets. Usually no criminal implication; it just suggests strong bonding and togetherness.
Examples
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After just a few weeks on the team, Maya and Priya were thick as thieves, finishing each other’s sentences.
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My brother and I used to be thick as thieves when we were kids, always getting into trouble together.
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Ever since they started working the night shift together, those two have been thick as thieves.
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At the conference, Jordan and Lee became thick as thieves and ended up planning a whole project over coffee.
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Don’t worry about her fitting in—once she meets Hana, they’ll be thick as thieves.
Grammar & Usage Notes
Typically used predicatively after a linking verb: “They’re thick as thieves.” You can vary tense (“were/are”), but the comparison phrase is fixed; “thick with someone” is related but different.
Synonyms
- as thick as thieves
- joined at the hip
- inseparable
- best friends
- like two peas in a pod
Antonyms
- at odds
- distant
- estranged