Omniscient describes someone or something with unlimited knowledge or understanding.

// "You'll need to tell me when you don't understand something I've explained," Maria said. "I'm not omniscient, you know."

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"The Abrahamic faiths conceive of God as an omniscient creator and generally abjure gambling as a result; one of the first laws passed by the Puritans in the Massachusetts Bay Colony banned the possession of cards, dice, or gaming tables." — Idrees Kahloon, The New Yorker, 2 Sept. 2024

One who is omniscient literally knows all. The word omniscient traces back to two Latin roots: omni-, meaning "all" or "universally," and the noun scientia, meaning "knowledge." You will recognize omni- as the prefix that tells all in such words as omnivorous ("eating all," or in actual use, "eating both plants and animals") and omnipotent ("all-powerful"). Scientia comes from the Latin verb scīre, meaning "to know," which likewise has a number of other knowledge-related descendants in English, including conscience, science, and prescience (meaning "foreknowledge").