slacken

verb

slack·​en ˈsla-kən 

slackened; slackening ˈsla-kᵊn-iŋ 

transitive verb

1

: to make less active : slow up

slacken speed at a crossing

2

: to make slack (as by lessening tension or firmness)

slacken sail

intransitive verb

1

: to become slack or slow or negligent : slow down

2

: to become less active : slack

Synonyms of slacken

• loosen

Choose the Right Synonym for slacken

delay, retard, slow, slacken, detain mean to cause to be late or behind in movement or progress.

delay implies a holding back, usually by interference, from completion or arrival.

bad weather delayed our arrival

retard suggests reduction of speed without actual stopping.

treatment that retards tumor growth

slow and slacken also imply a reduction of speed, slow often suggesting deliberate intention,

she closed her eyes and slowed her breathing

slacken an easing up or relaxing of power or effort.

on hot days runners slacken their pace

detain implies a holding back beyond a reasonable or appointed time.

unexpected business had detained her

Examples of slacken in a Sentence

Sales show no sign of slackening.

As he began to relax, his grip on the steering wheel slackened.

The captain ordered us to slacken the sails.

Recent Examples on the Web

On DeFilippis’s stage (kept effectively earthy and stark by scenic designer Ashley Basile), the stakes are ratcheted up from the jump and the tension never slackens. —Sara Holdren, Vulture, 23 Mar. 2026

Electromagnetism and the weak interaction intensify, while the strong force slackens. —Quanta Magazine, 11 Mar. 2026

In order to be more confident in predicting an El Niño, trade winds blowing from east-to-west across the equator would need to slacken, allowing more warm water from the western Pacific to push east and emerge at the surface. —Andrew Freedman, CNN Money, 10 Mar. 2026

The pacing slackens a little as the complicated process inches forward, but the ending tugs the heartstrings in enormously satisfying ways. —David Rooney, HollywoodReporter, 10 Mar. 2026

Word History

First Known Use

14th century, in the meaning defined at transitive sense 1

Rhymes for slacken

• blacken
• bracken
• lakin

Kids Definition

slacken

verb

slack·​en ˈslak-ən 

slackened; slackening -(ə-)niŋ 

1

: to make or become slower or less energetic

slacken speed

2

: to make less taut : loosen

slacken sail

3

: to become careless