Yechidah (Hebrew YChDH, “only one”) in Kabbalistic theory is the highest aspect of the human soul corresponding to the first Sephirah Kether, and is included in the neshamah. The yechidah closely corresponds to the Neoplatonist concept of the scintilla or synteresis, the spark of divine light at the center of the self. A.G.H.
Greer, John Michael. The New Encyclopedia of the Occult. St. Paul, MN, Llewellyn Worldwide. p. 524