D defs.my
Entry 1 sense Webster, 1913

Hourglass

/ou'-ẽrg-lăsˌ/ · Hour·glass · IPA /ˈaʊəɡlɑːs/
01 n. An instrument for measuring time, especially the interval of an hour. It consists of a glass vessel having two compartments, from the upper…
  1. 1.
    An instrument for measuring time, especially the interval of an hour. It consists of a glass vessel having two compartments, from the uppermost of which a quantity of sand, water, or mercury occupies an hour in running through a small aperture unto the lower.