Moving recklessly fast, as in Out the door she went, hell-bent for leather. The use of hell-bent in the sense of “recklessly determined” dates from the first half of the 1800s. Leather alludes to a horse's saddle and to riding on horseback; this colloquial expression may be an American version of the earlier British army jargon hell for leather, first recorded in 1889.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
How to use hell-bent for leather in a sentence
A second later he had hoisted her to his saddle-bow and was spurring hell-bent-for-leather for the open country.Rung Ho! | Talbot Mundy
But there are little meteors—very tiny ones—that come in, hell-bent-for-leather, at a shade less than the velocity of light.Hanging by a Thread | Gordon Randall Garrett