• رُكَام
• مَّرْكُوم
• يَرْكُمَهُۥ

Appears 3 times in the Quran.

1. 8:37 لِيَمِيزَ ٱللَّهُ ٱلْخَبِيثَ مِنَ ٱلطَّيِّبِ وَيَجْعَلَ ٱلْخَبِيثَ بَعْضَهُۥ عَلَىٰ بَعْضٍ فَيَرْكُمَهُۥ جَمِيعًا فَيَجْعَلَهُۥ فِى جَهَنَّمَ أُو۟لَٰٓئِكَ هُمُ ٱلْخَٰسِرُونَ

   That Allah might separate the impure from the good, and put the impure, some of it upon the other, and pile it up together, then cast it into hell; these it is that are the losers.
   

2. 24:43 أَلَمْ تَرَ أَنَّ ٱللَّهَ يُزْجِى سَحَابًا ثُمَّ يُؤَلِّفُ بَيْنَهُۥ ثُمَّ يَجْعَلُهُۥ رُكَامًا فَتَرَى ٱلْوَدْقَ يَخْرُجُ مِنْ خِلَٰلِهِۦ وَيُنَزِّلُ مِنَ ٱلسَّمَآءِ مِن جِبَالٍ فِيهَا مِنۢ بَرَدٍ فَيُصِيبُ بِهِۦ مَن يَشَآءُ وَيَصْرِفُهُۥ عَن مَّن يَشَآءُ يَكَادُ سَنَا بَرْقِهِۦ يَذْهَبُ بِٱلْأَبْصَٰرِ

   Do you not see that Allah drives along the clouds, then gathers them together, then piles them up, so that you see the rain coming forth from their midst? And He sends down of the clouds that are (like) mountains wherein is hail, afflicting therewith whom He pleases and turning it away from whom He pleases; the flash of His lightning almost takes away the sight.
   

3. 52:44 وَإِن يَرَوْا۟ كِسْفًا مِّنَ ٱلسَّمَآءِ سَاقِطًا يَقُولُوا۟ سَحَابٌ مَّرْكُومٌ

   And if they should see a portion of the heaven coming down, they would say: Piled up clouds.