Grammar term · Sarf · morphology
إِدْغَام
idgham
Assimilation (idgham)
Sarf · morphologyMorphophonemic processadvanced term6,989+ in the Qur'an
In one line
Merging twins: a silent letter folds into an identical vowelled one and a shadda marks the join — يَرْتَدِدْ becomes يَرْتَدَّ.
Classical definition
الإِدْغَامُ إِدْخَالُ حَرْفٍ سَاكِنٍ فِي حَرْفٍ مُتَحَرِّكٍ مِنْ جِنْسِهِ فَيَصِيرَانِ حَرْفًا مُشَدَّدًا، كَمَدَّ أَصْلُهُ مَدَدَ.
“Idgham is the entering of a vowel-less letter into a vowelled letter of the same kind so that they become one emphasised letter.”
(بتصرف من شذا العرف)
Key words in the Arabic
إِدْخَالinserting, folding into
مِنْ جِنْسِهِof the same kind
Understand it
Arabic will not pronounce dal-sukun-dal when it can say دّ: wherever two identical letters meet with the first silent, they fuse and the shadda records it. This is the engine behind the whole mudaaf class (مَسَّ = مَسَسَ), behind Form VIII fusions like اتَّقَى, and — in recitation — behind the tajwid rules that carry the same name. When jazm would force the twins apart, both faces appear in the Qur'an: يَرْتَدَّ merged, يَرْتَدِدْ unmerged.
How to spot it
Recognition test
A shadda where the wazn expects two separate identical letters: idgham. Unfold it to weigh the word correctly — رَدَّ weighs فَعَلَ, not فَعْلَ.
In the Qur'an
وَمَن يَرْتَدَّ مِنكُمْ عَن دِينِهِۦ
Al-Baqarah 2:217 — “And whoever of you renounces their faith”
يَرْتَدَّ = يَرْتَدِدْ with the two dals fused under the shadda — idgham holding even in jazm.
Forms it takes
فيه إدغام حرفين متماثلين ساكن ومتحركفيه إدغام حرفين متماثلين متحركينوفيه إدغام حرفين متماثلين ساكن ومتحركوفيه إدغام حرفين متماثلين متحركين
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