From Longman Dictionary of Contemporary Englishhourglasshour‧glass /ˈaʊəɡlɑːs $ ˈaʊrɡlæs/ noun [countable] 1 
TMCa glass container for measuring time in which sand moves slowly from the top half to the bottom in exactly one hour → egg-timer2 → hourglass figure
TMCa glass container for measuring time in which sand moves slowly from the top half to the bottom in exactly one hour → egg-timer2 → hourglass figureExamples from the Corpus
hourglass• Like sand in an hourglass, simultaneously pulled in both directions by the mysterious appetite of a two-headed gravity.• I picture the evolution of human consciousness in the shape of an hourglass.• The sand has run out of the hourglass. 