priestess n.

Middle English prēst, "cleric ranking below a bishop and above a deacon, a parish priest," from Old English preost, which probably was shortened from the older Germanic form represented by Old Saxon and Old High German prestar, Old Frisian prestere, all from Vulgar Latin *prester "priest," from Late Latin presbyter "presbyter, elder," from Greek presbyteros "elder (of two), old, venerable," comparative of presbys "old" (see presby-).

In Middle English also used generally for any man holding high Church office or anyone duly authorized to be a minister of sacred things; from c. 1200 of pagan and Muslim religious leaders. In the Old Testament sense (Old English), it is a translation of Hebrew kohen, Greek hiereus, Latin sacerdos.

fem. suffix, from French -esse, from Late Latin -issa, from Greek -issa (cognate with Old English fem. agent suffix -icge); rare in classical Greek but more common later, in diakonissa "deaconess" and other Church terms picked up by Latin.