The suffix became generalized for the formation of fem. derivs. of masc. sbs., e.g. F. comtesse (f. comte), whence Eng. countess, and similarly duchess, hostess, lioness, mistress, princess. In OF. -esse was added to mascs. in -ere, -eor, e.g. enchanteresse enchantress; so in ME. -ess was added to agent-nouns in -er and -ster, as huntress, seamstress, songstress, contraction taking place where possible; the older †governeresse was reduced to governess; there are several cases of sbs. in -tor with fems. in -tress (e.g. actress, benefactress, traitress), with the result that this ending corr. to F. -trice, L. -trix. There was gen. extension to other kinds of sb., as authoress, goddess, mayoress, poetess, prioress, for some of which, however, there are F. models.
"-ess." The Concise Oxford Dictionary of English Etymology. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/ess-1
"-ess." The Concise Oxford Dictionary of English Etymology. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/ess-1