ا ح دʾ-ḥ-d
— أَحَدaḥad: one; the lexicographers state that its original form is وَحَدwaḥad (root w ḥ d), the wāw having been changed to hamzah. This root occurs 85 times in the Quran: 74 times as أَحَدaḥad and 11 times as إِحْدَيiḥdā.(1) As a numeral, in which case the plural is āḥād and أُحْدَانuḥdān. For God, the use of "أَحَدaḥad" is more eloquent than "وَاحِدwāḥid": ﴿قُلْ هُوَ اللّٰهُ أَحَدٌ﴾ (Al-Ikhlāṣ 112:1)(2) As an adjective of generality, in contexts of negation, interrogation and condition, meaning "any one at all"; in this case it negates every kind of association. ﴿وَلَمْ يَكُنْ لَّهُۥ كُفُوًا أَحَدٌ﴾ (Al-Ikhlāṣ 112:4)
إِحْدَيiḥdā: feminine of أَحَدaḥad. ﴿اِنَّهَا لَاِحْدَي الْكُبَرِ﴾ (Al-Muddaththir 74:35)