A doubled quadriliteral follows an A–B–A–B radical sequence: the first equals the third, and the second equals the fourth.
صَمْصَمَ has ص م ص م, repeating ṣād and mīm alternately.
حَصْحَصَ has ح ص ح ص, repeating ḥāʾ and ṣād in the same alternating order.
This differs from the doubled triliteral, where only the second and third radical positions are identical. A quadriliteral doubled root contains two matched pairs, not just one adjacent pair.
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Doubled Quadriliteral Roots
The Seven Morphological Classes: Sound, Hamzated, Weak and Doubled
A doubled quadriliteral follows an A–B–A–B radical sequence: the first equals the third, and the second equals the fourth.
صَمْصَمَ has ص م ص م, repeating ṣād and mīm alternately.
حَصْحَصَ has ح ص ح ص, repeating ḥāʾ and ṣād in the same alternating order.
This differs from the doubled triliteral, where only the second and third radical positions are identical. A quadriliteral doubled root contains two matched pairs, not just one adjacent pair.