• أَجْدَر
• جِدَار
• جُدُر

Appears 4 times in the Quran.

1. 9:97 ٱلْأَعْرَابُ أَشَدُّ كُفْرًا وَنِفَاقًا وَأَجْدَرُ أَلَّا يَعْلَمُوا۟ حُدُودَ مَآ أَنزَلَ ٱللَّهُ عَلَىٰ رَسُولِهِۦ وَٱللَّهُ عَلِيمٌ حَكِيمٌ

   The dwellers of the desert are very hard in unbelief and hypocrisy, and more disposed not to know the limits of what Allah has revealed to His Messenger; and Allah is Knowing, Wise.
   

2. 18:77 فَٱنطَلَقَا حَتَّىٰٓ إِذَآ أَتَيَآ أَهْلَ قَرْيَةٍ ٱسْتَطْعَمَآ أَهْلَهَا فَأَبَوْا۟ أَن يُضَيِّفُوهُمَا فَوَجَدَا فِيهَا جِدَارًا يُرِيدُ أَن يَنقَضَّ فَأَقَامَهُۥ قَالَ لَوْ شِئْتَ لَتَّخَذْتَ عَلَيْهِ أَجْرًا

   So they went on until when they came to the people of a town, they asked them for food, but they refused to entertain them as guests. Then they found in it a wall which was on the point of falling, so he put it into a right state. (Musa) said: If you had pleased, you might certainly have taken a recompense for it.
   

3. 18:82 وَأَمَّا ٱلْجِدَارُ فَكَانَ لِغُلَٰمَيْنِ يَتِيمَيْنِ فِى ٱلْمَدِينَةِ وَكَانَ تَحْتَهُۥ كَنزٌ لَّهُمَا وَكَانَ أَبُوهُمَا صَٰلِحًا فَأَرَادَ رَبُّكَ أَن يَبْلُغَآ أَشُدَّهُمَا وَيَسْتَخْرِجَا كَنزَهُمَا رَحْمَةً مِّن رَّبِّكَ وَمَا فَعَلْتُهُۥ عَنْ أَمْرِى ذَٰلِكَ تَأْوِيلُ مَا لَمْ تَسْطِع عَّلَيْهِ صَبْرًا

   And as for the wall, it belonged to two orphan boys in the city, and there was beneath it a treasure belonging to them, and their father was a righteous man; so your Lord desired that they should attain their maturity and take out their treasure, a mercy from your Lord, and I did not do it of my own accord. This is the significance of that with which you could not have patience.
   

4. 59:14 لَا يُقَٰتِلُونَكُمْ جَمِيعًا إِلَّا فِى قُرًى مُّحَصَّنَةٍ أَوْ مِن وَرَآءِ جُدُرٍۭ بَأْسُهُم بَيْنَهُمْ شَدِيدٌ تَحْسَبُهُمْ جَمِيعًا وَقُلُوبُهُمْ شَتَّىٰ ذَٰلِكَ بِأَنَّهُمْ قَوْمٌ لَّا يَعْقِلُونَ

   They will not fight against you in a body save in fortified towns or from behind walls; their fighting between them is severe, you may think them as one body, and their hearts are disunited; that is because they are a people who have no sense.