سُقْيًا
Translation: May you be given water / refreshment!
سُقْيًا: accusative maṣdar used as an absolute object of an understood, conventionally omitted verb.
Understood: سَقَاكَ اللَّهُ سُقْيَا; Allah is subject and -ka the direct object.
The standalone accusative maṣdar is not a nominative subject; the implicit verb governs it.
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The Accusatives: Al-Mafʿūl al-Muṭlaq
سُقْيًا
Translation: May you be given water / refreshment!
سُقْيًا: accusative maṣdar used as an absolute object of an understood, conventionally omitted verb.
Understood: سَقَاكَ اللَّهُ سُقْيَا; Allah is subject and -ka the direct object.
The standalone accusative maṣdar is not a nominative subject; the implicit verb governs it.