split second

Noun

split-second (plural split-seconds)

1. (attributive) A stopwatch with two second hands, each of which may be stopped separately to time the intervals of a race by a sportsperson, or to time more than one sportsperson.
2. A fraction of a second; hence (figurative, also attributive) a very short time period; an instant, a moment.
   • It's very dangerous, though, when a man thinks for a split second that he understands death.1912, G[ilbert] K[eith] Chesterton, “The Eye of Death; or, The Murder Charge”, in Manalive, New York, N.Y.: John Lane, →OCLC, part II (The Explanations of Innocent Smith), page 182

   Synonyms:

   bat of an eye, bit, blink of an eye, crack, eyeblink, flash, glimpse, half a mo, instant, jiff