1. To do something in a sudden, fierce, and/or uncontrolled manner; to unleash something, especially that which is violent or destructive. The trapped wolf let loose a bone-chilling howl. The home team began to let loose an unwavering offensive barrage against their cross-town rivals. The owner of the ranch let his hounds loose upon the trespassers.

2. To allow something to spread, grow, or develop in a wild or uncontrolled manner, especially that which is destructive or ruinous. With news of the military junta's governmental overthrow, a wild, riotous pandemonium was let loose across the already unstable country.