Definition of "clepsydra"

"The dull, unflavoured drops from life's clepsydra".

1953, John Wyndham, The Kraken Wakes, page 124

They sat among the choiring clepsydras of the evening garden, time elapsing in a dozen ways, allowing their cigars to go out, keeping a companionable silence.

2006, Thomas Pynchon, Against the Day, Vintage, published 2007, page 856