thick as thieves
In real, traceable use. Part of the curated seed collection; community review is coming.
Meaning · English
Very close or friendly.
Where it’s used:
Used
Widespread English
Examples
He and Auntie Lou were thick as thieves at the moment.
Anyway, you're grown up now, it's not for you to be as thick as thieves with the likes of her.’
British National Corpus sentence via the MAGPIE corpus (CC BY 4.0, retrieved 2026-07-30)
Sources & notes
Listed in Wiktionary’s “English idioms” category (retrieved 2026-07-29); definition pending editorial review. Figurative class: Simile (PIE-English corpus, CC BY 4.0, retrieved 2026-07-31).
Common questions
What does “thick as thieves” mean?
Very close or friendly.
Is “thick as thieves” formal or informal?
No register label has been reviewed yet — treat it as neutral and check the usage notes above.