FromArabicمَدَّة(madda).

maddah (pluralmaddahs)

1. Arabicdiacritic similar in appearance to atilde. Over analif (آ(ʔā) "alif maddah"), it indicatesglottal stop, /ʔ/, followed by a long /aː/. The diacritic is not used separately, only over alif. Alif maddah can appear in the beginning:آسِف(ʔāsif) or in the middle of a word:قُرْآن(qurʔān).
2. In the Qur'an, it indicates an extra long vowel and can appear over any long vowel.
3. In Persian the letter is used only in the beginning of a word with a long /aː/:آمدن(âmadan).