An egg-timer, in the old kitchen sense, is a small hourglass: two glass bulbs with a thin neck, and sand that runs from the top to the bottom in about three or five minutes — the time many people want for a boiled egg. You turn it over when the water boils; when the sand has fallen, the egg is ready. That is the picture in learner dictionaries. In real kitchens the name has stretched: families also call a little wind-up dial or a beeping digital timer an egg-timer, even when there is no sand, as long as it is for a short wait. It is a homely, practical word, not a formal one.