Rule 5 allows initial wāw bearing ḍamma or kasra to be replaced by hamzah. The source calls this permissible (jāʾiz), not a change obligatory for every comparable word.
وُجُوهٌ ↔ أُجُوهٌ
Translation: Faces; two transmitted initial-letter variants.
وِشَاحٌ ↔ إِشَاحٌ
Translation: A sash / strap; the wāw and hamzah forms.
The condition relates to initial wāw, not to every wāw in a word.
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Rule 5: Optional Hamzah for Initial Wāw
Miscellaneous Morphological Explanations: Eight Rules for Wāw, Yāʾ, Alif and Hamzah
Rule 5 allows initial wāw bearing ḍamma or kasra to be replaced by hamzah. The source calls this permissible (jāʾiz), not a change obligatory for every comparable word.
وُجُوهٌ ↔ أُجُوهٌ
Translation: Faces; two transmitted initial-letter variants.
وِشَاحٌ ↔ إِشَاحٌ
Translation: A sash / strap; the wāw and hamzah forms.
The condition relates to initial wāw, not to every wāw in a word.