High Priestess (in the feminine form) or High Priest (in the masculine form) was a title used by a high ranking spiritual leader. This title was used among Omega IV natives, the Fabrini and Vulcan peoples.
According to the Omega IV Bible, Joshua was the high priest of the Jews in the second year of the reign of King Darius. He lived in the land of Judah and heard the prophecies of Haggai. (TOS: "The Omega Glory" text
According to the Book of the People, high priestesses were the only Fabrini individuals who could choose their own mates. In 2268, Natira held this position. (TOS: "For the World is Hollow and I Have Touched the Sky")
On Sigma Draconis VI, Kara served as the priestess leader of the Eymorgs. By command of the Ancients, only the pristess leader could operate the Great Teacher. (TOS: "Spock's Brain")
In 2285, T'Lar held the title of high priestess when she presided at the altar on Mount Selaya and was responsible for performing Spock's fal-tor-pan ritual: the returning his katra from Leonard McCoy. (Star Trek III: The Search for Spock)
A Vulcan high priestess was present for the birth of Spock and responsible for his delivery from Amanda Grayson in 2230. (Star Trek V: The Final Frontier)
The applications of the title to the above Vulcans were referenced only in the respective film's scripts.