Arabic mahrajān 'festival' started out as the name of one Persian feast, Mehregān

The usual Arabic word for an organised festival is mahrajān (مهرجان, also pronounced mihrajān). The Cairo International Film Festival is Mahrajān al-Qāhira al-Sīnimāʾī al-Duwalī, and in Arabic the Cannes festival is Mahrajān Kān. Feast days are still ʿīd.

It's borrowed from Persian Mehregān (Middle Persian mihragān), the feast of Mehr day in the month of Mehr, which falls in early October. Classical Arabic had no g, so the g became j, as Persian g usually did. Persian gowhar "jewel" became Arabic jawhar the same way.

The word is in Arabic by the 800s, and al-Fayyūmī's 14th-century dictionary defines it narrowly, as a festival of the Persians. I couldn't find a source that dates the shift to the general sense.

The Persian name is Mehr plus the suffix -agān, and Mehr is Mithra, whose name most scholars take to be the Indo-Iranian word for "contract". In modern Persian, mehr means love or kindness.

Two things I liked. Writers in Arabic, al-Bīrūnī among them, explained mihrajān as mihr + jān, "love of the soul", a folk etymology that works on the Arabic spelling, where -gān had become -jān. And the borrowing runs the other way too: Persian took eyd "holiday" from Arabic ʿīd, while its own word for a film festival is jashnvāre.

I came across this while putting together something on the Persian month names. Corrections are welcome, especially on the dating.

https://redd.it/1wtygip
@r_etymology