ن ک سn-k-s
(ن) نَكَسَ يَنْكُسُ نَكْسًاnakasa yankusu naksan: to turn upside down, to invert; passive voice: to be turned upside down, to be turned back on one's heels (in argument). ﴿ثُمَّ نُكِسُوْا عَلٰى رُءُوْسِهِمْ﴾ (Al-Anbiyāʾ 21:65)
نَاكِسٌnākis pl. نَاكِسُوْنَnākisūna (active participle, ism fāʿil): one who hangs (his head). Only once in the Quran: ﴿وَلَوْ تَرٰٓى اِذِ الْمُجْرِمُوْنَ نَاكِسُوْا رُءُوْسِهِمْ عِنْدَ رَبِّهِمْ﴾ (As-Sajdah 32:12)
Form II (tafʿīl) نَكَّسَ يُنَكِّسُ تَنْكِيْسًاnakkasa yunakkisu tankīsan: to turn back gradually, to return (one's powers) step by step to weakness. Only once in the Quran: ﴿وَمَنْ نُّعَمِّرْهُ نُنَكِّسْهُ فِي الْخَلْقِ﴾ (Yā Sīn 36:68)