From yada'; properly, a knowing one; specifically, a conjurer; (by impl) a ghost -- wizard.
see HEBREW yada'
H3049. yiddeoni
יִדְּעֹנִי noun masculine familiar spirit (properly either as knowing, wise (acquainted with secrets of unseen world), Ew vielwisserisch; or as intimate acquaintance of soothsayer, see RSJPh xiv. 1885. 127) — absolute יִדְּעֹנִי Deuteronomy 18:11 2t.; plural יִדְּעֹנִים 1 Samuel 28:3 6t.; מִן הַיִּדְּעֹנִי 28:9, read מִן הַיִּדְּעֹנִים (see ᵐ5 Th We Klo Dr); familiar spirit, always "" אֹבוֺת אוֺב, 28:3, 9; Isaiah 8:19; 19:3; 2 Kings 21:6 (אוֺב עשׂה; "" עוֺנֵן נִחֵשׁ,) = 2 Chronicles 33:6; 2 Kings 23:24; Leviticus 19:31; 20:6, 27 (all H; on last two compare Acts 16:16 and DrDeuteronomy 18:11), 18:11("" אוֺב + אֶלהַֿמֵּתִים דֹּרֵשׁ).