A split second is an extremely short moment — less than a second, so short you could not really measure it. 'For a split second I thought it was my brother.' You use it for something that happened almost too fast to notice, or for a moment of thought or feeling that came and went instantly.

A split second is split second 是 an extremely short moment極短的一瞬 — less than a second不到一秒， so short短到 you could not really measure it你根本沒辦法真的去量它。'For a split second I thought it was my brother.'有一瞬間，我以為那是我哥。You use it你用它 for something that happened almost too fast to notice說快到幾乎來不及注意就發生的事， or for或用在 that came and went instantly一閃即逝的 a moment of thought or feeling一個念頭或感覺上

It is also used as an adjective before a noun, and there it means 'made or done in that tiny moment, and needing to be exactly right': a split-second decision, split-second timing. That adjective often carries a little admiration — it says the timing was so fine that being slightly late would have ruined it.

It它 also也 as an adjective當形容詞 before a noun用在名詞前面， and there it means那時它的意思是 'made or done in that tiny moment, and needing to be exactly right'「在那一瞬間做出來、而且必須分毫不差」： a split-second decision瞬間的決定、 split-second timing分毫不差的時機。That adjective這個形容詞 often常常 carries a little admiration帶著一點佩服 — it says它是在說 the timing was so fine那時機抓得那麼準， that being slightly late稍微晚一點 would have ruined it就全毀了

The phrase came from a kind of stopwatch with two hands, one of which could be stopped on its own to catch an in-between time; the second hand was 'split'. As a noun it is usually written as two words, and as an adjective before a noun, with a hyphen.

The phrase這個說法 came from來自 a kind of stopwatch一種碼錶： with two hands它有兩根針， one of which其中一根 could be stopped on its own可以單獨停下 to catch an in-between time去抓中間的時間； the second hand秒針 was 'split'是被「分開」的。As a noun當名詞時 it它 usually通常 as two words寫成兩個字， and as an adjective before a noun當名詞前的形容詞時， with a hyphen加連字號