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]

WordNet (r) 3.0 (2006):

sprue
    n 1: a chronic disorder that occurs in tropical and non-tropical
         forms and in both children and adults; nutrients are not
         absorbed; symptoms include foul-smelling diarrhea and
         emaciation [syn: sprue, tropical sprue, psilosis]