م س وm-s-w
(ن) مَسَا يَمْسُوْ مَسْوًاmasā yamsū maswan: to reach evening. (This verb is not used in the Quran.)
Form IV (ifʿāl) اَمْسٰى يُمْسِيْ اِمْسَاءًamsā yumsī imsāʾan: to enter upon the evening; it is also one of the defective (incomplete) verbs (afʿāl nāqiṣah), meaning «to become», as well as a complete verb. Only once in the Quran: ﴿فَسُبْحٰنَ اللّٰهِ حِيْنَ تُمْسُوْنَ وَحِيْنَ تُصْبِحُوْنَ﴾ (Ar-Rūm 30:17) — i.e. when you enter the evening and when you enter the morning.