Source : Webster's Revised Unabridged Dictionary (1913)

Four-way \Four"-way`\, a.
   Allowing passage in either of four directions; as, a four-way
   cock, or valve. --Francis.

   {Four-way cock}, a cock connected with four pipes or ports,
      and having two or more passages in the plug, by which the
      adjacent pipes or ports may be made to communicate;
      formerly used as a valve in the steam engine, and now for
      various other purposes. In the illustration, a leads to
      the upper end of a steam engine cylinder, and b to the
      lower end; c is the steam pipe, and d the exhaust pipe.