هُوَ is a pronoun referring back to a known referent.
كَمْ asks for a number or expresses abundance.
كَيْتَ وَذَيْتَ stand in for an unspecified utterance or event.
These expressions can all function as nouns in grammatical classification, but they do very different semantic and syntactic jobs.
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Al-Kināyāt — Kam, its Tamyīz and Syntactic Positions
هُوَ is a pronoun referring back to a known referent.
كَمْ asks for a number or expresses abundance.
كَيْتَ وَذَيْتَ stand in for an unspecified utterance or event.
These expressions can all function as nouns in grammatical classification, but they do very different semantic and syntactic jobs.