A word that means "all-knowing," this is usually applied to God.
Problems with Omniscience
There is some dispute about what "all" actually means. Does God literally know everything, not only that has happened, but that also might happen? If so, then in what sense does free will exist? If all your decisions are known by God before you make them then it's not clear if you are really making any "choices" since all the things that you do are predestined.
In a universe with a truly omniscient God, the Calvinist doctrine of predestination would have to be true. This carries its own set of issues, as it implies that God intentionally creates people already knowing that they will wind up in hell.