slacken

Verb
  1. Become slow or slower (synset 200441535)
    "Production slowed"
  2. Make less active or fast (synset 200442167)
    "He slackened his pace as he got tired"; "Don't relax your efforts now"
  3. Become looser or slack (synset 200422361)
    "the rope slackened"
  4. Make slack as by lessening tension or firmness (synset 200422078)

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