from The Century Dictionary.
- noun A mounted groom who follows his master when on horseback.
Sorry, no etymologies found.
Washball, Charley Joyce, and Sam Sloman, riding well in the first flight of second horsemen -- his lordship's pad-groom, Mr. Fossick's man in drab with a green collar, Mr. Wake's in blue, also a lad in scarlet and a flat hat, with a second horse for the huntsman.
Springwheat, from the window; and just at the moment the pad-groom emerged from the house, and ran to his lordship's horse's head.