as thick as thieves
Meaning
Very close friends; strongly bonded and often sharing secrets or always together.
Origin
Recorded from the 19th century. "Thick" meant close/intimate, and thieves were stereotyped as working closely together in secretive partnership.
Notes
Usually means very close friends, but can also hint they’re conspiring or being secretive. Informal, common in speech and writing.
Examples
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Ever since they started the new job together, Maya and Jordan have been as thick as thieves.
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My grandparents were as thick as thieves in college, and they’re still best friends decades later.
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The twins are as thick as thieves—they even finish each other’s sentences.
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After that road trip, we were as thick as thieves and kept laughing about our inside jokes.
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At school, Lina and Priya are as thick as thieves, so it’s hard to see one without the other.
Grammar & Usage Notes
Fixed simile pattern: "as thick as thieves" (not *the thieves*). Used after linking verbs: "are/were"; can modify a pair/group: "They’re as thick as thieves."
Synonyms
- very close
- inseparable
- like two peas in a pod
- joined at the hip
Antonyms
- at odds
- not on speaking terms
- distant