slacken

To gradually decrease in intensity or tautness; to become slack; to lag.

The pace slackened.

He seemed tired, and the Rat let him rest unquestioned, understanding something of what was in his thoughts; knowing, too, the value all animals attach at times to mere silent companionship, when the weary muscles slacken and the mind marks time.

To make slack, less taut, or less intense.

slacken the rope

During this interlude, Warwick, though he had slackened his pace measurably, had so nearly closed the gap between himself and them as to hear the old woman say, with the dulcet negro intonation: […]

To deprive of cohesion by combining chemically with water; to slake.

to slacken lime