From Longman Dictionary of Contemporary Englishegg-timerˈegg-ˌtimer noun [countable] DFUa small glass container with sand in it that runs from one part to the other in about three or five minutes, used for measuring the time it takes to boil an egg
Examples from the Corpus
egg-timer• Joyce's family is numbered with the grains of sand in a thousand egg-timers. 