Webster's Revised Unabridged Dictionary · 1913

Unbridled

Unbridled , adjective

[Prefix un- not + bridled.]

Loosed from the bridle, or as from the bridle; hence, unrestrained; licentious; violent; as, unbridled passions.
Unbridled boldness. — B. Jonson
Lands deluged by unbridled floods. — Wordsworth