The Collaborative International Dictionary
Arithmancy \Ar"ith*man`cy\, n. [Gr. ? number + -mancy.] Divination by means of numbers.
Douglas Harper's Etymology Dictionary
"divination by numbers," 1570s, from Greek arithmos "number" (see arithmetic) + -manteia "divination" (see -mancy).
Wiktionary
n. divination using numbers that are the equivalent of letters of a name
Wikipedia
In modern numerological terminology, arithmancy (a shortened form of Greek ἀριθμομαντεία divination by numbers) is a form of divination based on assigning numerical value to a word or phrase, by means of a simplified version of ancient Greek isopsephy or Hebrew/Aramaic gematria, as adapted to the Latin alphabet. Arithmancy is associated with the Chaldeans, Platonists, Pythagoreans, and the Kabbalah.
Usage examples of "arithmancy".
Lily had done to get the number eleven, but at the flat he found her old Arithmancy text and quickly worked it out.
Maggie says that Arithmancy is just another form of Divination anyway, and one based on far more superstition than something like Astrology, which is very complex and requires much more in the way of calculations and knowledge of Astronomy.
His birthday is the ninth of July, which also fits the Arithmancy numbers.
Divination to keep practicing, but Hermione refused point-blank to skive off Arithmancy, and there was no point in staying without her.
Hermione, and she set off for Arithmancy, while Harry and Ron headed toward North Tower, and Divination.
Charms, Defense Against the Dark Arts, Transfiguration, Herbology, Arithmancy, Ancient Runes, and Potions, and shot off to a first period Ancient Runes class without further ado.
Ravenclaw, Harry found himself walking down to dinner alone from the common room, Ron having rushed off into a nearby bathroom to throw up yet again, and Hermione having dashed off to see Professor Vector about a mistake she thought she might have made in her last Arithmancy essay.
Hermione was immediately cleared to continue with Charms, Defense Against the Dark Arts, Transfiguration, Herbology, Arithmancy, Ancient Runes, and Potions, and shot off to a first period Ancient Runes class without further ado.
A few days before the match against Ravenclaw, Harry found himself walking down to dinner alone from the common room, Ron having rushed off into a nearby bathroom to throw up yet again, and Hermione having dashed off to see Professor Vector about a mistake she thought she might have made in her last Arithmancy essay.