A unit of time equal to one second (1 s); used to express a very short duration.
彼は一秒の差で勝利を逃した。
He missed victory by one second.
あと一秒でも早ければ間に合ったのに。
If only it had been one second earlier, we would have made it.
この反応は一秒以内に起こる。
This reaction occurs within one second.