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WordNet
slack up

v. make less active or fast; "He slackened his pace as he got tired"; "Don't relax your efforts now" [syn: slack, slacken, relax]

Usage examples of "slack up".

He paid out line and let me pull, then cut retros and ate the slack up plus more, reeling me in like a deep-sea catch.

Micum tightened his grip on the rope, but Seregil surfaced and motioned for him to slack up again.

He pumped so hard that Decker was sure the rod would snap, then Skink would slack up, reel fast, and pump again.