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 a split second it felt like I had neither.

From The Wall Street Journal • Jan. 8, 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

The lawyer who represented his family at his inquest, Gareth Naylor, tells the BBC that in a "split second" of an adult leaving the room, the toddler climbed on a bed and fell.

From BBC • Aug. 13, 2025

He said in a split second, after spotting the Israeli missile, he reacted and somehow survived.

From Slate • Jun. 14, 2025

For a split second, the world seems to tilt on its axis, like it’s about to roll right off its designated ring in the solar system and float aimlessly into outer space.

From "I Can Make This Promise" by Christine Day

Related Words

• blink of an eye
• millisecond
• nanosecond