Other forms: stopwatches
A stopwatch is the timer coaches click to measure exactly how long something takes. Start the stopwatch, a stopwatch in hand, stop the stopwatch.
The mechanical kind reads to a tenth of a second and the electronic to a hundredth, but human reaction adds about two tenths at each end, which is why serious athletics uses electronic timing rather than a hand-held stopwatch.
1nounstopwatchA timer clicked to measure exactly how long something takes.
“The coach held up a stopwatch and timed each swimmer over one length of the pool.”
stopwatch is a timer.
Stop plus watch, from the nineteenth century, when a watch that could be halted and restarted was a novelty.
From stop + watch.
Etymology from Wiktionary, CC BY-SA