stopwatch

noun

A watch that can be started and stopped to measure exactly how much time has passed.

Example sentences

“The coach timed each lap with a stopwatch.”
“Press the button on the stopwatch the moment the swimmer touches the wall.”

One word. The verb phrase is 'time someone with a stopwatch', or just 'time someone'.

Related words

scoreboardA big display at a game or competition that shows how many points each side has.shinguardA protective pad worn over the front of the lower leg, especially during sports.dugoutA low, sheltered bench area beside a sports field where coaches and substitute players sit during a match.mouthguardA protective piece, usually plastic, worn inside the mouth to cover the upper or lower teeth, or both.sidelineA boundary line running along the edge of something, such as a sports field.gogglesProtective glasses with a flexible frame that fits tightly around the eyes.