the.com/sandglass

means A device with two glass bulbs joined at a narrow neck, through which sand trickles at a fixed rate to measure a set interval of time.

from A straightforward compound of 'sand' and 'glass,' naming the thing by what it's made of and what fills it — related to the hourglass, which got its name once such devices were standardized to mark a full hour. The design itself is old, with uncertain origins, though it's known to have been used by sailors to time shifts and ring ship's bells, since, unlike water clocks, sand doesn't freeze or slosh on a rolling deck.