divination by the use of numbers, especially by the number of letters in names.

Also a·rith·mo·man·cy [uh-rith-muh-man-see, ar-ith-] /əˈrɪθ məˌmæn si, ˈær ɪθ-/.

Origin of arithmancy

1570–80; < New Latin arithmomantia < Greek arithmó(s) number + manteía -mancy Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Word Origin and History for arithmancy

"divination by numbers," 1570s, from Greek arithmos "number" (see arithmetic) + -manteia "divination" (see -mancy).

Online Etymology Dictionary, © 2010 Douglas Harper