Quote
Figured I'd pitch in, if that's alright SH

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

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

A-hunting we will go.
A-hunting we will go.
We'll catch a fox
And put 'im in a box
And never let 'im go.
Tantivy, tantivy, tantivy,
A-hunting we will go.