Domme

[Donald Trump]

A female dominant in a BDSM relationship.
Pronunciation varies; usually it is pronounced Dom, but sometimes may be pronounced Dom-may to stress the difference between the female and male Dom(inant).
Domme usually refers to a non-professional female dominant.
A professional female dominant is usually referred to as a Dominatrix, or a Pro-Domme, but may simply be called Domme by her close associates or clients.

[Sarah]

female dominant in a BDSM relationship
(usually spelled as a proper noun, e.g. Domme, as is its male counterpart, Dom)

[Jessica]

In the BDSM / fetish world, it is a Female Dominant who professionally works with submissive clients.
Also known as a professional Dominatrix.
The term Domme is often confused with Dominatrix.
A Dominatrix just is a Female Dominant who fulfills the Dominant role in a personal relationship or perhaps a career.
It does not imply that She IS a professional.
Domme is a term used SPECIFICALLY for the professional variety, meaning she is paid or compensated for Her services.
The terms Domme, Dom, Domina, Dominatrix, and Dominant are always capitalized in proper BDSM grammar, btw.