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1. To become less tense or taut; to become slack. As the wind died away, the sheets of the mainsail slackened off and the boat slowed to a drift.
2. To cause something to become more slack. In this usage, a noun or pronoun can be used between "slacken" and "off." The captain ordered the seaman to slacken off the line. The cord is wound too tight. We'll need to slacken it off if we're going to untangle the animals.
3. To decrease in intensity or activity. Most of the businesses on the island close up for the year once the summer business starts to slacken off toward the end of August. The winds began slackening off as the hurricane shifted course out to sea.
4. To cause something to become less intense or active. In this usage, a noun or pronoun can be used between "slacken" and "off." I slackened off my speed as I went round the tight bend on the treacherous mountain road. If the government slackens these regulations off, the economy is going to head straight back into a recession in a few years' time.
See also: off
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.