For the use of the word in the Harry Potter books, see Hogwarts subjects - Arithmancy. In modern
numerological terminology, arithmancy (a shortened form of Greek αριθμομαντεια divination by numbers) is a simplified version of ancient Greek
Isopsephy or Hebrew/Aramaic
Gematria, as adapted to the Latin alphabet.
See more at Wikipedia.org...
Ancient study of the magical properties of numbers.