wheelhorse

noun

1. (US, dated)One of a team of horses which is nearest to the wheels of a carriage, as opposed to a leader or forward horse.

   “The off wheel-horſe a grey, named Single Peeper, ſold for 50 [guineas] […] The near wheel-horſe cheſnut, named Chance.”

   “The driver […] neither knew any thing, said any thing, or did any thing but watch a dozen equine ears, and keep six reins taut in his hands, and coax the off wheel[-]horse with the belly of his whip-lash every two minutes, invariably accompanying the stroke with a tremendous solitary cluck.”

   ““Ay! he med well say that,” repeated the wagoner, still digesting the pleasure of Ben Lee’s compliment, and slapping the wheel[-]horse’s vast flank, so that the fairy chime began again, and the smack resounded like an accompaniment to its music.”

   “In contrast to the methods used in New England all the lumber from the high Sierras is taken out in the summer instead of the winter. Teams of about seven pairs of horses, or mules, or traction engines, are used. Teams draw two or three wagons, and are managed by one driver who rides on a wheelhorse and guides with one rein, whip and voice.”

   “The cannoneer posted nearest the left wheel of the limber engages the end of the pole of his carriage in the pole ring of the neck yoke and then hitches the near wheel horse; the cannoneer posted nearest the right wheel of the limber hitches the off wheel horse.”

2. (US, figuratively)A person who labors heavily for a particular cause, without being concerned about recognition.

   “[F]rom his [Benjamin Ruggles'] well-known habits of industry and constant devotion to the interests of his constituents, he was called "The Wheelhorse of the Senate."”

   “A medical journal, it seems to the writer, should be a medium for the propagation of useful knowledge, the instruction of the profession in the best and most scientific methods of fighting disease; and who is so well qualified for the work as the old wheelhorses, the men who have grown gray in the fight?”

   “I can't understand why an old wheel-horse like Elsworth should kick over the traces that way.”

   “He was a wheelhorse, a tower of strength, to the Park Service and to the forces that were trying to establish new parks, seashores, canoe wildernesses, and other reservations during the Kennedy and Johnson years.”

3. (historical, obsolete)A foot-propelled vehicle; a bicycle.

   “As in most other accomplishments, practice alone can make a skilful rider of velocipedes. The tyro can, however, profit by the experience of others, and I give a few rules for his guidance, as well as directions for his practice. The first point is to gain confidence in, and familiarity with, his wheel horse.”