He who is single, absolutely without partner or equal in His essence, attributes, actions, names and decrees.
“O People of the Book! commit no excesses in your religion: nor say of Allah aught but the truth. Christ Jesus the son of Mary was (no more than) A Messenger of Allah, and His Word, which He bestowed on Mary, and a Spirit proceeding from Him: so believe in Allah and His Messengers. Say not “Trinity”: desist: it will be better for you: FOR ALLAH IS ONE GOD: GLORY BE TO HIM: (FAR EXALTED IS HE) ABOVE HAVING A
SON. To Him belong all things in the heavens and on earth. And enough is Allah as a Disposer of affairs.”
(4:171)The Holy Quran

From the root w-h-d with the classical Arabic connotations: to be one, to be made one, to be called one to connect, join, unite to be unique, singular to be one apart from others.
Allah is starting point from which all else has arisen.
He is the source of all creation. His unity includes all that appears as diverse, separate or individual.
