He who is present everywhere, at any moment and observes, knows all things.
“There is no god but He: THAT IS THE WITNESS OF ALLAH, His angels, and those endued with knowl- edge, standing firm on justice. There is no god but He the Exalted in Power, the Wise. The religion before Allah is Islam (submission to His Will): nor did the people
of the Book dissent therefrom except through envy of each other, after knowledge had come to them. But if any deny the Signs of Allah, Allah is swift in calling to account.”
(3:18-19) The Holy Quran
From the root sh-h-d with the classical Arabic connotations: to bear witness to offer testimony to have knowledge of, to experience.