-mancy

Also ‑mantic and ‑mancer.

Divination.

Greek manteia, divination.

Though many words exist in this ending, most are rare; among common ones are geomancy and necromancy. For details, and more commonly encountered ones, Some have corresponding adjectives in ‑mantic (geomantic, necromantic) and a few have related forms in ‑manter for a person who practices divination in that way (cartomancer, necromancer).

Some words seem to include this ending through an accident of spelling: adamancy, dormancy, and others contain ‑cy but not ‑mancy.

Examples of words in -mancy
Word origins are from Greek.

aeromancy

prediction by observing weather conditions

aēr, air

arithmancy

divination using numbers, especially by counting the number values of letters in names

arithmos, number

bibliomancy

telling the future by interpreting a randomly chosen passage from a book, especially the Bible

biblion, book

cartomancy

fortune telling by interpreting a random selection of playing cards

French carte, card

chiromancy

the prediction of a person's future from the lines on the palms of their hands; palmistry

kheir, hand

geomancy

divination from the configuration of a handful of earth or random dots

gē, earth

hydromancy

foretelling the future using a reflective object or surface, such as that of water in a bowl; scrying

hudōr, water

necromancy

communicating with the dead, especially in order to predict the future; more generally, witchcraft, sorcery, or black magic

nekros, corpse

oneiromancy

the interpretation of dreams in order to foretell the future

oneiros, dream

pyromancy

divination by fire or by forms appearing in fire

pur, fire