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1.                 From The Collaborative International Dictionary of English v.0.48:
                   
   
   
                   
                     
   Sprue \Sprue\ (spr[udd]), n. [Etymol. uncertain.]
      1. (Founding)
         (a) Strictly, the hole through which melted metal is
             poured into the gate, and thence into the mold.
         (b) The waste piece of metal cast in this hole; hence,
             dross.
             [1913 Webster]
      2. (Med.) Same as Sprew.
         [1913 Webster]