There is the verb quicken to make something quick or faster, but Merriam-Webster doesn't list slowen. What is the verb to make something slow (as in 'reduce in speed', not 'something that is slow')?


6 Answers 6


The word slow itself can be used as a verb. It is an antonym for quicken

Slow, from M-W

to make (something, such as a car) move at a lower speed; to begin to move at a lower speed; to become slower

"the car slowed to a halt"

  • 3
    "The driver slowed his car to a halt" as an example of the transitive use
    – blgt
    Mar 1, 2016 at 9:31

You can also technically use "retard", but people will probably more often associate this with mental disability.

Retard, from M-W

to slow down the development or progress of (something)

  • 3
    "Retard" as a verb, clearly applied to an inanimate object, might still work.
    – Chris H
    Mar 1, 2016 at 8:55
  • 6
    @Chenmunka My immediate reaction with full context was No, so trust me, especially in the UK, it's not an acceptable synonym.
    – deworde
    Mar 1, 2016 at 9:32
  • 4
    I am from the UK and retard is an entirely unacceptable term, used exclusively as an offensive word for people with mental disabilities. I suspect Chenmunka is used to interacting only with a small subset of the population (academics maybe?), for I can assure you that among the "common" people, retard is very definitely an insult first and foremost.
    – Benubird
    Mar 1, 2016 at 9:47
  • 4
    @user568458 In line with your idea, I think it entirely depends on context. E.g. "We erected a barrier to retard the spread of the contagion." I don't think it necessarily has to be a technical context, but the use of retard as a non-pejorative definitely has a more formal feel to it in my opinion. I doubt anyone is going to interpret retard as an insult in the example I gave. Mar 1, 2016 at 9:47
  • 4
    I'm surprised no one has mentioned the difference in pronunciation. When used as a verb (and similar), I'm accustomed to having the emphasis on the second syllable, whereas the noun/epithet has emphasis on the first syllable. I think that lessens the likelihood of confusion. (That still leaves the matter of taste, but that's a different issue.) Mar 1, 2016 at 22:36

If you mean to actively intervene and make something else slower, you can use impede. From Merriam-Webster:


To slow the movement, progress, or action of (someone or something)

Transitive verb - To interfere with or slow the progress of

  • He claims that economic growth is being impeded by government regulations.
  • The soldiers could not impede the enemy's advance.

For example, you could say "We thought that hiring more staff would quicken progess on this project, but actually, the extra hassle has impeded us".

This is a good choice if you want to emphasise that one thing is making another, different, separate thing slower (as opposed to something slowing naturally).

It's often used for abstract things. For example, "to impede progress" is a pretty common phrase.

  • "hinder" and "hindered" are probably the more commonly used synonyms of impede.Or, at least in the UK.
    – Dan
    Mar 1, 2016 at 14:42
  • I considered adding "hinder" but I think it's a little closer to "interfere with" than "slow down" - hindering something could mean harming its quality as well as its speed. But they are very similar. Mar 1, 2016 at 15:01

Consider, hamper

To slow the movement, progress, or action of (someone or something.)

Construction is hampering traffic on the highway.


  • 1
    Best choice for non-physical movement.
    – A.S.
    Mar 1, 2016 at 10:12

There is also decelerate, which is the opposite of accelerate.

From M-W

to move slower : to lose speed



It has the effect of slowing down.

Merriam Webster Dictionary

Examples of brake in a sentence. Can be used as a transitive verb.

I had to brake suddenly when a cat ran in front of the car.

Braked the car sharply when someone pulled out in front of us.

  • Welcome to English Language & Usage. This answer was flagged as low-quality because of its length and content. Can you try to include reference or link (that can support your answer) and its essential part? Please take the tour and visit our help center for additional guidance.
    – user140086
    Mar 1, 2016 at 11:02

Not the answer you're looking for? Browse other questions tagged or ask your own question.