(ن، ض) نَكَلَ يَنْكُلُ نُكُوْلًاnakala yankulu nukūlan: to draw back (from something out of fear), to desist; hence «نَكَالnakāl»: a punishment that deters others (from the same crime). (This verb is not used in the Quran.)
نَكَالٌnakāl (noun, ism dhāt): exemplary punishment. ﴿فَجَعَلْنٰهَا نَكَالًا لِّمَا بَيْنَ يَدَيْهَا وَمَا خَلْفَهَا﴾ (Al-Baqarah 2:66); ﴿جَزَآءًۢ بِمَا كَسَبَا نَكَالًا مِّنَ اللّٰهِ﴾ (Al-Māʾidah 5:38)
نِكْلٌnikl pl. اَنْكَالٌankāl (noun, ism dhāt): heavy fetter (which keeps a prisoner from fleeing). Only once in the Quran: ﴿اِنَّ لَدَيْنَآ اَنْكَالًا وَّجَحِيْمًا﴾ (Al-Muzzammil 73:12)
Form II (tafʿīl) نَكَّلَ يُنَكِّلُ تَنْكِيْلًاnakkala yunakkilu tankīlan: to inflict exemplary punishment repeatedly. Only once in the Quran: ﴿وَاللّٰهُ اَشَدُّ بَاْسًا وَّاَشَدُّ تَنْكِيْلًا﴾ (An-Nisāʾ 4:84)