slacken

verb3

1. •
   To gradually decrease in intensity or tautness; to become slack; to lag.

   • The pace slackened.
2. •
   To make slack, less taut, or less intense.

   • 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: […] — 1900
3. •
   To deprive of cohesion by combining chemically with water; to slake.