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

For very small particles, the entire event lasts only a split second before the material completely burns up.

From Science Daily • May 14, 2026

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

From Barron's • Apr. 27, 2026

These monumental changes arrived in a split second, and I’ve replayed the fall in my mind countless times.

From The Wall Street Journal • Feb. 26, 2026

Boone sprinted onto the piano and launched into the air above May, and in a split second, it was over.

From Los Angeles Times • Dec. 23, 2025

She turned to Max, and somehow in that split second, she could see him as the kindergartener he’d once been, as well as the teenager he was about to become.

From "The School for Whatnots" by Margaret Peterson Haddix

Related Words

• blink of an eye
• millisecond
• nanosecond