يَا زَيْدَانِ!
Translation: O two Zayds!
يَا: particle.
زَيْدَانِ: dual vocative built on alif in accusative position; dual nūn is retained.
The alif resembles the dual nominative sign, but this is a fixed vocative form occupying the accusative position.
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Al-Munādā: Vocative Types and Rules
يَا زَيْدَانِ!
Translation: O two Zayds!
يَا: particle.
زَيْدَانِ: dual vocative built on alif in accusative position; dual nūn is retained.
The alif resembles the dual nominative sign, but this is a fixed vocative form occupying the accusative position.