Definition of "wheelhorse"

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

1750 October, “A Description, with the Form, of the Four Wheel Carriage, which was Drawn at Newmarket, 19 Miles in 54 Minutes. […] Invented by Mr J. Wright in Long Acre.”, in Sylvanus Urban [pseudonym; Edward Cave], editor, The Gentleman’s Magazine, and Historical Chronicle, volume XX, London: Printed by Edw[ard] Cave, at St John's Gate, published January 1755, page 440

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.

1869 September, E. P. Willard, “A Night and a Day on the Sierra Nevada”, in The Western Monthly, volume II, number 9, Chicago, Ill.: Reed, Browne & Co., publishers, No. 18 Tribune Building, page 179, column 2

“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.

1886, Maxwell Gray [pseudonym; Mary Gleed Tuttiett], chapter I, in The Silence of Dean Maitland: A Novel, London: Kegan Paul & Co.; republished New York, N.Y.: D. Appleton and Company, 1888, part I, page 12

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.

1914 April, W[illard] W[ebster] Eggleston, “A Trip to Stanislaus Forest, California. (Abstract.)”, in Bulletin, number 9, Burlington, Vt.: Published annually by the [Vermont Botanical] Club; Free Press Printing Company, page 23

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.

1916, War Department, Office of the Chief of Staff, “The Driver”, in Provisional Drill and Service Regulations for Field Artillery (Horse and Light) 1916 (War Department Document; no. 538), Washington, D.C.: Government Printing Office, part III (Mounted Instruction), section IV (Mounted Instruction), paragraph 437, page 181

[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."

1866, Charles Lanman, “Ruggles, Benjamin”, in Dictionary of the United States Congress, Compiled as a Manual of Reference for the Legislator and Statesman, 3rd rev. edition, [Washington, D.C.]: Government Printing Office, page 326, column 1

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?

1905 December, E. E. Lusk, “Homeopathy ‘is Not Built that Way’”, in H. C. Allen, editor, The Medical Advance and Journal of Homeopathics: A Monthly Journal of Hahnemannian Homeopathy, volume XLIII, number 12, Batavia, Ill.: James E. Forrest, page 768

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

1910 November, Jack London, Theft: A Play in Four Acts, New York, N.Y.: The Macmillan Company; London: Macmillan & Co., Act I, page 3

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.

1997, David Backes, A Wilderness Within: The Life of Sigurd F. Olson, Minneapolis, Minn.: University of Minnesota Press, page 369

In 1830 a bold and vigorous attempt was made to utilize the wheel-horse. A French post-office official, M. Dreuze by name, brought forward an improvement on the old two-wheel velocipede, which bid fair to be successful. […] A number of the country letter-carriers were mounted on the wheel-horse, and whilst the roads continued dry and hard M. Dreuze could congratulate himself on the success of his invention; but with wet weather came bad roads, and to the wet succeeded frost and snow. A little extra labour was all that was required to overcome the extra friction of the bad roads, but the wheels refused to progress on the slippy frozen surface.

1869, Velox [pseudonym], “The Velocipede of the Past”, in Velocipedes, Bicycles, and Tricycles: How to Make and How to Use Them. With a Sketch of their History, Invention, and Progress, London: George Routledge and Sons, The Broadway, Ludgate; New York, 416, Broome Street, pages 39–40

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.

1869, Velox [pseudonym], “The Art of Velocipede Management”, in Velocipedes, Bicycles, and Tricycles: How to Make and How to Use Them. With a Sketch of their History, Invention, and Progress, London: George Routledge and Sons, The Broadway, Ludgate; New York, 416, Broome Street, page 77; reprinted in “Velocipedes. The Velocipede of the Day.”, in Edmund Routledge, editor, Routledge’s Every Boys Annual: An Entertaining Miscellany of Original Literature, London: George Routledge and Sons, The Broadway, Ludgate; New York, 416, Broome Street, 1870, page 414