slack up

verb

To become slack; slacken.

Similar
slackslackenrelax
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Meanings

verbslack up (third-person singular simple present slacks up, present participle slacking up, simple past and past participle slacked up)

present singular third person slacks up · participle present slacking up · participle past slacked up · past slacked up

  1. idiomaticintransitiveTo become slack; slacken.

    […] he was rnnning toward the girl; […] he looked right toward her; he slacked up a little, and then started off on a run; don't know whether he saw me or not.

    1877, Rowland Cox, The American Law Times (volume 4, page 414)
  2. idiomaticintransitiveTo slack; to let one's standards slip.

Synonyms & antonyms

verbmake less active or fast

Similar
slackslackenrelax
Broader
decreaselessenminify
Also see
relaxslackslacken

Synonym sets from Open English WordNet, CC BY 4.0.

Cite this entry
APA

slack up. (n.d.). In WatkinsX Dictionary. Retrieved November 4, 2026, from https://dictionary.watkinsx.com/word/slack%20up

MLA

“slack up.” WatkinsX Dictionary, https://dictionary.watkinsx.com/word/slack%20up. Accessed November 4, 2026.

Chicago

WatkinsX Dictionary, s.v. “slack up,” accessed November 4, 2026, https://dictionary.watkinsx.com/word/slack%20up.

Source: slack up on Wiktionary, CC BY-SA 4.0.