ک و رk-w-r
(ن) كَارَ يَكُوْرُ كَوْرًاkāra yakūru kawran (original form: كَوَرَkawara): to wind, to wrap in layers like a turban (this verb is not used in the Quran).
Form II (tafʿīl) كَوَّرَ يُكَوِّرُ تَكْوِيْرًاkawwara yukawwiru takwīran: to wind up thoroughly. Three times in the Quran: ﴿إِذَا الشَّمْسُ كُوِّرَتْ﴾ (At-Takwīr 81:1) — and the surah takes its name from it; also ﴿يُكَوِّرُ الَّيْلَ عَلَي النَّهَارِ وَيُكَوِّرُ النَّهَارَ عَلَي الَّيْلِ﴾ (Az-Zumar 39:5) — i.e. He wraps the night over the day, which has been understood as a subtle allusion to the roundness of the earth.