Tafsir of At-Tur 52:9

يَوْمَ تَمُورُ‌ السَّمَاءُ مَوْرً‌ا (...the Day when the sky will tremble, a horrible trembling, ...52:9) The lexicographical denotation of the word mawr is violent shaking, or movement caused by unrest. This verse describes the violent movement of the heavens on the Day of Resurrection.