1. To reduce the compact nature of something or to make something less tight or not as firm: Sarah used a spade to loosen the soil in the backyard.

After eating so much, Marvin had to loosen his belt.

One of the screws on the table had loosened and so it had to be tightened again.

2. To become or to cause something to become less strict: They should loosen up on the restrictions that the law has imposed regarding driving on the road between the two towns.
3. To undo, to untie, or to unfasten something: Please loosen the knot of the rope that is keeping the gate closed.