The Collaborative International Dictionary of English v.0.48:

Watershoot \Wa"ter*shoot`\, n.
   1. A sprig or shoot from the root or stock of a tree. [Obs.]
      [1913 Webster]

   2. (Arch.) That which serves to guard from falling water; a
      drip or dripstone.
      [1913 Webster]

   3. A trough for discharging water.
      [1913 Webster]