(س) نَسِيَ يَنْسٰى نَسْيًا وَنِسْيَانًاnasiya yansā nasyan wa-nisyānan: not to retain something, to forget it intentionally or unintentionally; also to disregard. ﴿نَسُوا اللّٰهَ فَنَسِيَهُمْ﴾ (At-Tawbah 9:67); ﴿رَبَّنَا لَا تُؤَاخِذْنَآ اِنْ نَّسِيْنَآ اَوْ اَخْطَاْنَا﴾ (Al-Baqarah 2:286)
نَسْيٌnasy (verbal noun, maṣdar, also a noun, ism dhāt): a forgotten (worthless) thing; مَنْسِيٌّmansiyy (passive participle, ism mafʿūl): forgotten. Only once in the Quran, in the words of Mary (peace be upon her): ﴿وَكُنْتُ نَسْيًا مَّنْسِيًّا﴾ (Maryam 19:23)
نَسِيٌّnasiyy (adjective on the pattern of فَعِيْلٌfaʿīl): very forgetful. ﴿وَمَا كَانَ رَبُّكَ نَسِيًّا﴾ (Maryam 19:64)
Form IV (ifʿāl) اَنْسٰى يُنْسِيْ اِنْسَآءًansā yunsī insāʾan: to make someone else forget something. ﴿فَاَنْسٰىهُمْ اَنْفُسَهُمْ﴾ (Al-Ḥashr 59:19); ﴿وَمَآ اَنْسٰنِيْهُ اِلَّا الشَّيْطٰنُ﴾ (Al-Kahf 18:63)