One; Alone. Ihdahunna: One of the women. Ihadi: One of the two. Ihda: One. Ahad: One; Alone. This word is applied to Allah alone and signifies The One, The Sole, who has been and will ever be and Alone, who has no second to share in his lordship nor in His Essence.The Holy Quran has used two different words to express the Unity of God, Ahad and Wahid. The former denotes the absolute Unity of God without relation to any other being, while the latter means the first or the starting point followed by a second and a third.
The word Ahad has been used in the Quran 82 times
Thus the Divine attribute of Wahid (One) is Intended to show that God is the only source from which all creation springs. Although none of his creatures is similar to him, and he is independent of all, yet everything does point to him, just as a second or third thing necessarily points to the first. Whereas Ahad signifies Oneness of God in His person, the idea of a second being inconceivable, Wahid signifies uniqueness of God in His attributes. Thus the expressions Allahu Wahidun A would mean that Supreme Being Who is the Source of law, from Whom all creation had emanated and Allahu Ahad means that Allah is that Being Who is One and Alone in the sense that when we think of Him the very idea that there is any other being or thing is absent altogether from our minds. He is One and Alone in every sense. Nothing is like Him, nor is He like anything else.
Say: "He is Allah, The One (Ahad). Allah, the Self-Sufficient Master. He begets not, nor is he begotten. And there is none coequal or comparable to Him." Surah Al-Ikhlas (The Purity)