The Collaborative International Dictionary of English v.0.48:

Stopcock \Stop"cock`\, n.
   1. A bib, faucet, or short pipe, fitted with a turning
      stopper or plug for permitting or restraining the flow of
      a liquid or gas; a cock or valve for checking or
      regulating the flow of water, gas, etc., through or from a
      pipe, etc.
      [1913 Webster]

   2. The turning plug, stopper, or spigot of a faucet. [R.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

stopcock
    n 1: faucet consisting of a rotating device for regulating flow
         of a liquid [syn: stopcock, cock, turncock]