Hell-for-leather Definition

hĕlfər-lĕthər
adjective
With all of one's energy, will, etc.; with wholehearted or reckless determination.
Webster's New World
At full speed or with great speed.
A hell-for-leather chase.
Webster's New World
adverb
In a hell-for-leather manner or fashion.
Webster's New World
As fast as possible; recklessly fast.
He rode hell-for-leather to catch up with the stagecoach.
Wiktionary

Less common form of hell-for-leather.

Wiktionary