1Seated on or provided with a good horse, bicycle, etc.
2Correctly, properly, or skilfully positioned, fixed, fitted, set, etc.; having a good mounting or setting.
3Of a theatrical production, film, etc.: successfully or pleasingly staged, produced, directed, etc.
Early 16th century; earliest use found in 2nd Baron Berners (c1467–1533), soldier, diplomat, and translator. From well + mount + -ed.