slough vs sump

slough

noun
  • A state of depression. 

  • A small pond, often alkaline, many but not all formed by glacial potholes. 

  • Dead skin on a sore or ulcer. 

  • A muddy or marshy area. 

  • A type of swamp or shallow lake system, typically formed as or by the backwater of a larger waterway, similar to a bayou with trees. 

  • The skin shed by a snake or other reptile. 

  • A secondary channel of a river delta, usually flushed by the tide. 

verb
  • To shed (skin). 

  • To slide off (like a layer of skin). 

  • To discard. 

  • To commit truancy, be absent from school without permission. 

sump

noun
  • An intentional depression around a drain or scupper that promotes drainage. 

  • The crankcase or oil reservoir of an internal combustion engine. 

  • The lowest part of a mineshaft into which water drains. 

  • A hollow or pit into which liquid drains, such as a cesspool, cesspit or sink. 

  • A completely flooded cave passage, sometimes passable by diving. 

  • The pit at the lowest point in a circulating or drainage system (FM 55-501). 

verb
  • Of a cave passage, to end in a sump, or to fill completely with water on occasion. 

How often have the words slough and sump occurred in a corpus of books? (source: Google Ngram Viewer )