the GNU version of the Collaborative International Dictionary of English
n. A woman skilled in equestrianism; a horsewoman.
The Century Dictionary and Cyclopedia
n. A female rider or performer on horseback.
Word Usage
"Nor could he fail, as she crossed the floor, to see two women: one, the grand lady, the mistress of the Big House; one, the lovely equestrienne statue beneath the dull-blue, golden-trimmed gown, that no gowning could ever make his memory forget."