slacken
     v 1: become slow or slower; "Production slowed" [syn: {slow}, {slow
          down}, {slow up}, {slack}]
     2: make less active or fast; "He slackened his pace as he got
        tired"; "Don't relax your efforts now" [syn: {slack}, {slack
        up}, {relax}]
     3: become looser or slack; "the rope slackened"
     4: make slack as by lessening tension or firmness [syn: {remit}]
Source: WordNet® 2.0