A device, mechanism, or substance that causes something to slow down or reduce in speed.
From decelerate (de- plus celerare) plus the agent suffix -or (Latin -or, meaning one who does). Emerged in 20th-century scientific and mechanical terminology.
In particle physics, scientists use decelerators to slow down subatomic particles so they can study them—it's like the opposite of what a particle accelerator does, and both are crucial for understanding matter.
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