• تَسْتَتِرُونَ
• سِتْر
• مَّسْتُور

Appears 3 times in the Quran.

1. 17:45 وَإِذَا قَرَأْتَ ٱلْقُرْءَانَ جَعَلْنَا بَيْنَكَ وَبَيْنَ ٱلَّذِينَ لَا يُؤْمِنُونَ بِٱلْءَاخِرَةِ حِجَابًا مَّسْتُورًا

   And when you recite the Quran, We place between you and those who do not believe in the hereafter a hidden barrier;
   

2. 18:90 حَتَّىٰٓ إِذَا بَلَغَ مَطْلِعَ ٱلشَّمْسِ وَجَدَهَا تَطْلُعُ عَلَىٰ قَوْمٍ لَّمْ نَجْعَل لَّهُم مِّن دُونِهَا سِتْرًا

   Until when he reached the land of the rising of the sun, he found it rising on a people to whom We had given no shelter from It;
   

3. 41:22 وَمَا كُنتُمْ تَسْتَتِرُونَ أَن يَشْهَدَ عَلَيْكُمْ سَمْعُكُمْ وَلَآ أَبْصَٰرُكُمْ وَلَا جُلُودُكُمْ وَلَٰكِن ظَنَنتُمْ أَنَّ ٱللَّهَ لَا يَعْلَمُ كَثِيرًا مِّمَّا تَعْمَلُونَ

   And you did not veil yourselves lest your ears and your eyes and your skins should bear witness against you, but you thought that Allah did not know most of what you did.