Definition of "mule"

One day he ran into a herd of a half dozen elk, so he rode his mule down the canyon three or four miles, leaving the sheep alone.

2017, Robert S. McPherson, Cowboying In Canyon Country, Dog Ear Publishing, page 200

It would be exceedingly interesting to know if the hybrid would reproduce, a matter I deem exceedingly doubtful, for the chances are it would prove a "mule" (infertile).

1922, Onnie Warren Smith, The Book of the Pike, page 187

Vegetable mules supply an irrefragable argument in favour of the sexual system of botany.

1789, Erasmus Darwin, The Loves of the Plants, J. Johnson, page 149

The most extraordinary mule, however, that is asserted to have been produced on the Continent, is a cross between the cabbage and horse-radish, which Monsieur Sageret reports that he has obtained […]

1837, William Herbert, Amaryllidaceæ: Preceded by an Attempt to Arrange the Monocotyledonous Orders, and Followed by a Treatise on Cross-bred Vegetables, and Supplement, page 353

"Where in the hell do you think I learned to be such a mule?”

2005, Dorothea Benton Frank, Isle of Palms, Penguin

Cocaine packet ingestion (these patients referred to as “mules”) may warrant surgery, Golytely or expectant passage.

2006, “Gastroenterology: Esophageal Foreign Bodies”, in Steven E. Diaz, The Little Black Book of Emergency Medicine (Jones and Bartlett's Little Black Book Series), 2nd edition, Sudbury, MA: Jones and Bartlett Publishers, page 101

“Yeah, in Denver, we know about Uriarte's involvement in meth. Our Las Cruces office seized over six hundred pounds of methamphetamine from two of his mules last year.”

2007, Thomas G. Blacklock, Safe Zone: A Novel Approach to the Drug War, Xlibris Corporation, page 44

What is less clear, however, is why mint workers should have chosen to produce mules, if they were making forgeries […]

1988, Andrew Burnett, The Normanby hoard and other Roman coin hoards, British Museum Publications

He was in the middle of organizing his massive stash of rare and exquisite bounty, all kept safely in the inventory cache of a mule, an entirely separate character which he paid a monthly fee to maintain exclusively for that purpose.

2007, David L. McClard, Verotopia Online: The MMORPG of the Century‎, Xlibris, page 89

In heavier seas where a boat must sail a course dictated by waves, or where wave action makes power more important than pointing, the mule will prove the faster sail.

1974, Yachting, volume 135, page 60

There are many drug lords, each with his own corridor (think of it as a franchise of sorts) funneling narcotics into Texas. There are multifold methods of transport. The old, and still viable, way is to "mule" it across the Rio Grande in a small boat.

2000, Arturo Longoria, Keepers of the Wilderness

Thornton was supposed to mule it back to the States from one of the ports he stopped in, give it to Maxwell and Ames, and get the second half of a quarter-million.

2004, William Glenn, The Sailor's Death

The bride was a shocking housekeeper and dragged round all day in boudoir cap, frowsy negligee and mules—slip, slop, slip, slop.

1944, Emily Carr, “First Tenant”, in The House of All Sorts‎

Routine dress for Tuesday will be bra and panties with high-heel satin mules.

1946, George Johnston, Skyscrapers in the Mist, page 29