Meaning
Very close friends who share confidences and keep company constantly; intimate to the point of exclusivity, sometimes with a hint of conspiracy. Informal, and usually built with 'be' or 'become' ('they're as thick as thieves'). Nothing to do with stupidity - the 'thick' here is an older sense of the word meaning closely allied. Informal and warm in tone; the 'thick' is closeness, not stupidity, a distinction sometimes missed. Regional use: General English (British in origin).
Origin
'Thick' has meant 'intimately allied' since the 18th century: Richard Twining's memoir (1781) records 'He and I were quite thick.' Earlier similes for closeness included 'as thick as inkle weavers', 'as thick as peas in a shell' and 'as thick as three in a bed', all now obsolete. The phrase originated as 'as thick as two thieves', playing on thieves as the archetypal conspirators - sharing secrets and canting slang, as 17th- and 18th-century dictionaries of thieves' language attested. The first print example known to The Phrase Finder is a letter dated March 1827, published in February 1828 in The Morning Chronicle: 'Bill Morris and me are as thick as two thieves.' The Old Bailey trial records, which go back to 1674, do not contain the phrase until 1874.
Research Sources
References used to check this entry’s meaning, history, or documented forms.
Variants
- as thick as two thieves
- be as thick as thieves
- get as thick as thieves
- thick as thieves with someone
Usage Examples
- The two interns sat together at every lunch and were thick as thieves within a week.
- Ever since the chess tournament, my father and the next-door neighbour have been as thick as thieves.
- Do not worry about the new committee members; they are already thick as thieves with the chair.