The established adjective examples are أَكْبَرُ and أَحْمَرُ.
أَكْبَرُ → كُبْرَىٰ
أَحْمَرُ → حَمْرَاءُ
Their feminine forms are not made with round tā. Here the two causes are adjective status and the pattern of a verb.
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Route 2: An Adjective on a Verb Pattern
Cause of Ghayr Munsarif: The Pattern of a Verb
The established adjective examples are أَكْبَرُ and أَحْمَرُ.
أَكْبَرُ → كُبْرَىٰ
أَحْمَرُ → حَمْرَاءُ
Their feminine forms are not made with round tā. Here the two causes are adjective status and the pattern of a verb.