• سَدّ
• سَدِيد

Appears 5 times in the Quran.

1. 4:9 وَلْيَخْشَ ٱلَّذِينَ لَوْ تَرَكُوا۟ مِنْ خَلْفِهِمْ ذُرِّيَّةً ضِعَٰفًا خَافُوا۟ عَلَيْهِمْ فَلْيَتَّقُوا۟ ٱللَّهَ وَلْيَقُولُوا۟ قَوْلًا سَدِيدًا

   And let those fear who, should they leave behind them weakly offspring, would fear on their account, so let them be careful of (their duty to) Allah, and let them speak right words.
   

2. 18:93 حَتَّىٰٓ إِذَا بَلَغَ بَيْنَ ٱلسَّدَّيْنِ وَجَدَ مِن دُونِهِمَا قَوْمًا لَّا يَكَادُونَ يَفْقَهُونَ قَوْلًا

   Until when he reached (a place) between the two mountains, he found on that side of them a people who could hardly understand a word.
   

3. 18:94 قَالُوا۟ يَٰذَا ٱلْقَرْنَيْنِ إِنَّ يَأْجُوجَ وَمَأْجُوجَ مُفْسِدُونَ فِى ٱلْأَرْضِ فَهَلْ نَجْعَلُ لَكَ خَرْجًا عَلَىٰٓ أَن تَجْعَلَ بَيْنَنَا وَبَيْنَهُمْ سَدًّا

   They said: O Zulqarnain! surely Gog and Magog make mischief in the land. Shall we then pay you a tribute on condition that you should raise a barrier between us and them
   

4. 33:70 يَٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوا۟ ٱتَّقُوا۟ ٱللَّهَ وَقُولُوا۟ قَوْلًا سَدِيدًا

   O you who believe! be careful of(your duty to) Allah and speak the right word,
   

5. 36:9 وَجَعَلْنَا مِنۢ بَيْنِ أَيْدِيهِمْ سَدًّا وَمِنْ خَلْفِهِمْ سَدًّا فَأَغْشَيْنَٰهُمْ فَهُمْ لَا يُبْصِرُونَ

   And We have made before them a barrier and a barrier behind them, then We have covered them over so that they do not see.