Definition: the eldest female in a group; a woman who is the senior member, as in age or rank, of a group, class, profession, etc.
This is the feminine version of the more rare “doyen,” which means:
the senior member of a body or group
a person considered to be knowledgeable or uniquely skilled as a result of long experience in some field of endeavor
“Doyen” is Old French for “dean” which vaguely means leader.
Why I Looked It Up
In a book about the Vanderbilt family, I found this caption:
Caroline Astor, the doyenne of Gilded Age New York society.