The word originates from the Arabic: Mufti (مفتي) meaning an Islamic scholar. It has been used by the British Army since 1816 and is thought to derive from the vaguely Eastern style dressing gowns and tasselled caps worn by off-duty officers in the early 19th century. Yule and Burnell's Hobson-Jobson: A Glossary of Colloquial Anglo-Indian Words and Phrases, and of Kindred Terms, Etymological, Historical, Geographical and Discursive (1886) notes that the word was "perhaps originally applied to the attire of dressing-gown, smoking-cap, and slippers, which was like the Oriental dress of the Mufti".
A mufti day (also known as casual clothes day, casual Friday, colour day, own clothes day, home clothes day, plain clothes day, non-uniform day, mufting day, free dress day, civvies day, dress down day, uniform-free day) is a day where students and staff go to school in casual clothing instead of school uniform. This is found in many countries where students are required to wear uniform, including the United Kingdom, Ireland, Canada, Fiji, Australia, India, New Zealand, Nigeria, South Africa, Zimbabwe, Pakistan and Bangladesh.
- "civies - definition of civies by the Free Online Dictionary, Thesaurus and Encyclopedia". Thefreedictionary.com. Retrieved 2014-03-26.
- "MUFTY". Hobson Jobson Dictionary. Retrieved 2008-05-29.
- "What Is 'Mufti' In Mufti Day?". LBC. Retrieved 2019-06-06.
- "Mufti day gets a dressing down". The Sydney Morning Herald. 2004-02-18. Retrieved 2019-06-06.