abate (v)
die away (v)
let up (v)
slack (v)
slack off (v)

Definition: become less in amount or intensity
Example: The storm abated. The rain let up after a few hours.

let up (v)
ease up (v)
ease off (v)

Definition: reduce pressure or intensity
Example: he eased off the gas pedal and the car slowed down.

loose (v)
loosen (v)

Definition: make loose or looser
Example: loosen the tension on a rope.

unscrew (v)

Definition: loosen something by unscrewing it
Example: unscrew the outlet plate.