1 C1 informal
To reduce speed or slow down.
"The driver slacked up as the car approached the junction."
inseparable
slack up
C1 informal inseparable transitive/intransitive
To slow down, reduce speed or tension, or ease up on effort.
In plain English
To slow down or stop pulling so hard on something.
What does "slack up" mean?
2 meanings, ordered from most common to least. Color-coded by CEFR level.
2 C1 neutral
To release tension on a rope or line (nautical use).
"Slack up on the bowline before we try to move the sail."
inseparable
Literal vs figurative
Words literally mean
To bring something up to a slack (loose) state — to release tension.
Actually means
To slow down or stop pulling so hard on something.
Usage tip
Chiefly American dialectal or nautical English. In sailing, it means to loosen a rope. Rarely used in modern standard English; learners should prefer 'ease up' or 'let up'.
Words that pair with "slack up"
Natural word combinations native speakers use most often.
rope pace tension speed pressure
How to conjugate "slack up"
The five tense forms you'll use most often.
Base
slack up
I/you/we/they
3rd person
slacks up
he/she/it
Past simple
slacked up
yesterday
Past participle
slacked up
have + pp
-ing form
slacking up
continuous
Hear "slack up" in the wild
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