split second

American  

noun

1. a fraction of a second.

2. an infinitesimal amount of time; instant; twinkling.

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split second British  

noun

1. an extremely small period of time; instant

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adjective

1. made or arrived at in an infinitely short time

   a split-second decision

2. depending upon minute precision

   split-second timing

split second Idioms  

1. An instant, a fraction of a second, as in Our best swimmer came in a split second before theirs. This expression alludes to a stop watch that has two second hands, one above the other, for timing more than one athlete or intervals of a race by a single athlete. Each hand can be stopped independently of the other, so a second can be “split” when one second hand stops a fraction of a second after the other. [c. 1880]

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Other Word Forms

• split-second
  adjective

Etymology

Origin of split second

First recorded in 1880–85

Example Sentences

"It all happened so fast, in a split second," Sausan recounted.

From Barron's • Apr. 27, 2026

For a split second, the lights, the crowd and his energy aligned perfectly.

From Los Angeles Times • Dec. 23, 2025

In a split second, Claire picks up, gets in her car, and heads for the highway, leaving her family in the dust.

From Salon • Dec. 3, 2025

A split second after “Action!” was called, I darted across the hall to a better spot and ran through the frame.

From The Wall Street Journal • Oct. 7, 2025

It was like she read my mind, and I felt sorry for it because, for a split second, I’d wished she wasn’t there.

From "Hope Springs" by Jaime Berry

Related Words

• blink of an eye
• millisecond
• nanosecond