A muḍāʿaf (doubled) root contains two identical radicals in the relevant pattern. It is not merely any word that happens to have a written shaddah; the repeated letters belong to the root.
مَدَّ comes from م د د: the second and third radicals are both dāl.
رَدَّ comes from ر د د with the same repetition.
Shaddah represents an assimilated pair of consonants in pronunciation and writing. Although the surface spelling looks shorter, the three-root-letter analysis remains intact. Triliteral and quadriliteral doubling follow different arrangements.
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The Doubled Category
The Seven Morphological Classes: Sound, Hamzated, Weak and Doubled
A muḍāʿaf (doubled) root contains two identical radicals in the relevant pattern. It is not merely any word that happens to have a written shaddah; the repeated letters belong to the root.
مَدَّ comes from م د د: the second and third radicals are both dāl.
رَدَّ comes from ر د د with the same repetition.
Shaddah represents an assimilated pair of consonants in pronunciation and writing. Although the surface spelling looks shorter, the three-root-letter analysis remains intact. Triliteral and quadriliteral doubling follow different arrangements.