Slough, pronounced like slew, refers to a marshy place or mire.
As a verb, it can mean to plod through mud or for a slough to
engulf something. The word's origins are appropriately murky. It
derives from Middle English sloughe or slo, which comes from Old
English sloh, meaning muddy ground. After that the origins are
uncertain. It could derive from Middle High German slouche,
meaning ditch, or from Proto-Germanic *slokhaz. Figuratively,
slough describes a state of moral degradation. John Bunyan made
use of this meaning in The Pilgrim's Progress with the "Slough
of Despond," a deep bog into which Christian sinks under the
weight of sin and guilt. Then I stepped to him [Help] that
pluckt him [Christian] out, and said, Sir, wherefore, since over
this place is the way from the City of Destruction to yonder
Gate, is it that this plat is not mended, that poor travellers
might go thither with more security? And he said unto me, This
miry Slough is such a place as cannot be mended; it is the
descent whither the scum