arithmancy
Divination using numbers that are the equivalent of letters of a name
uncountable
Of this roote last spoken of [astrology], springs innumerable branches; such as the knowledge of natiuities; the Chiromancie, Geomantie, Hydromantie, Arithmantie, Physiognomie: & a thousand others: which were much practiced, & holden in great reuerence by the Gentiles of olde.
Where it comes from
From Ancient Greek ἀριθμός (arithmós, “number”) + -mancy.
Adapted from the Wiktionary entry arithmancy (CC BY-SA 4.0).