Why do we put ress at the end of some words, like actress, mayoress and murderess, but not for others like doctress, accountantress, or teacheress?

Question

Why do we put ress at the end of some words, like actress, mayoress and murderess, but not for others like doctress, accountantress, or teacheress?

In: 12609

Answer 1

Anything ending in -tor as the masculine should technically have -trix as the feminine version. But that has dramatically fallen out of favor in the modern English speaking world. So instead the masculine version is used for both male and female.

Fun fact. Bellatrix LeStrange from Harry Potter. Her name is the female of Bellator, meaning fighter/warrior.