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.
      [1913 Webster]

   2. The cistern or reservoir made at the lowest point of a
      mine, from which is pumped the water which accumulates
      there.
      [1913 Webster]

   3. A pond of water for salt works. --Knight.
      [1913 Webster]

   4. A puddle or dirty pool. [Prov. Eng.]
      [1913 Webster]

   Sump fuse, a fuse used in blasting under water.

   Sump men (Mining), the men who sink the sump in a mine.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sump
    n 1: an oil reservoir in an internal combustion engine
    2: a well or other hole in which water has collected
    3: a covered cistern; waste water and sewage flow into it [syn:
       cesspool, cesspit, sink, sump]

Moby Thesaurus II by Grady Ward, 1.0:

96 Moby Thesaurus words for "sump":
   artificial lake, baygall, bayou lake, bog, bottom, bottomland,
   bottoms, buffalo wallow, cesspool, cistern, cloaca, cloaca maxima,
   dam, dead water, dike, drain, dump, etang, everglade, farm pond,
   fen, fenland, fishpond, freshwater lake, garbage dump,
   glacial lake, glade, gutter, headchute, hog wallow, holm,
   inland sea, kennel, lagoon, laguna, lake, lakelet,
   landlocked water, linn, loch, lough, marais, marish, marsh,
   marshland, meadow, mere, millpond, millpool, mire, moor, moorland,
   morass, moss, mud, mud flat, nyanza, oxbow lake, peat bog, piscina,
   plash, pond, pondlet, pool, puddle, quag, quagmire, quicksand,
   reservoir, salina, salt marsh, salt pond, scupper, septic tank,
   sewer, sink, slob land, slough, sluice, sough, stagnant water,
   standing water, still water, swale, swamp, swampland, taiga, tank,
   tarn, tidal pond, volcanic lake, wallow, wash, water hole,
   water pocket, well