The Collaborative International Dictionary of English v.0.48:

Sump \Sump\, n. [Cf. G. sumpf a sump in a mine, a swamp, akin to
   LG. sump, D. somp a swamp, Dan. & Sw. sump, and perhaps to E.
   swamp.]
   1. (Metal.) A round pit of stone, lined with clay, for
      receiving the metal on its first fusion. --Ray.
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   2. The cistern or reservoir made at the lowest point of a
      mine, from which is pumped the water which accumulates
      there.
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   3. A pond of water for salt works. --Knight.
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   4. A puddle or dirty pool. [Prov. Eng.]
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   Sump fuse, a fuse used in blasting under water.

   Sump men (Mining), the men who sink the sump in a mine.
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