In the Chrestomanci series
" is one of the classifications of magic-user recognised in World 12A
of the Related Worlds
It is a specialty classification, and isn't part of the grading scale that includes "enchanter
" and "witch
Soothsayers presumably inhabit the ground left uncovered by Fortune-Tellers, Clairvoyants, and Diviners. Some use packs of cards equivalent to the Tarot cards of our world.