From Longman Dictionary of Contemporary Englishstopwatchstop‧watch /ˈstɒpwɒtʃ $ ˈstɑːpwɑːtʃ, -wɒːtʃ/ noun [countable] 
TMCa watch used for measuring the exact time it takes to do something, especially to finish a race
TMCa watch used for measuring the exact time it takes to do something, especially to finish a raceExamples from the Corpus
stopwatch• But seconds after Christopher slid from his chair, Brady clicked a stopwatch.• In this case, the setting of the edit-point on the source-tape is best done by stopwatch.• Had he not established it scientifically, through his stopwatch studies?• In 1883, Taylor had taken on an assistant, Emlin Hare Miller, to help with his stopwatch studies.• As I clicked my stopwatch at the start line it began to rain.• Perhaps the most invaluable feature is the unique cable control that allows you to activate the stopwatch from a tailored finger grip.• The answer was a hierarchical organization run by the timetable, the rule book, and the stopwatch.• Eventually the time had to be decided by the stopwatch of an arena judge. 