The one who has ever been and ever remains alone. The incomparable, unequalled, indivisible One.The Sole One.
The One who depends upon no other, and to whom there is no likeness. The one in whom all names, attributes and relationships are united.
“Say, He is Allah, ( who is ) One. Allah, the eternal refuge. He neither begets nor is born. Nor is there to Him any equivalent”
(112.1-4) The Quran
From the root a-h-d with the classical Arabic connotations: to be one,the only one, one alone, sole, to unite, unify.