tantivy

tantivy \tan-TIV-ee\, adjective:

1. Swift; rapid.

adverb:
1. At full gallop.

noun:
1. A rush, a gallop or stampede.

interjection:
1. (used as a hunting cry when the chase is at full speed.)

The passage of wild pigeons from this wood to that-with their slight tantivy-and carrier haste- Now from under some rotten stump your hoe turns up a spotted salamander- your own contemporary- A small trace of Egypt and the Nile in New England- Where is the priest of Isis.
-- Henry David Thoreau, Journal: 1842-1848

How does it come that a few short hours later we find him galloping tantivy over the dusty hills, no less than two hundred miles, as the birds fly, from the counter railings of welcomings?
-- Francis Lynde, Empire Builders

Tantivy, while associated with many aspects of horseback riding, is of unknown origin.