The Collaborative International Dictionary of English v.0.48:

Slough \Slough\, n. [OE. slogh, slough, AS. sl[=o]h a hollow
   place; cf. MHG. sl[=u]ch an abyss, gullet, G. schlucken to
   swallow; also Gael. & Ir. sloc a pit, pool. ditch, Ir. slug
   to swallow. Gr. ????? to hiccough, to sob.]
   1. A place of deep mud or mire; a hole full of mire.
      --Chaucer.
      [1913 Webster]

            He's here stuck in a slough.          --Milton.
      [1913 Webster]

   2. [Pronounced sl[=oo].] A wet place; a swale; a side channel
      or inlet from a river.

   Note: [In this sense local or provincial; also spelt sloo,
         and slue.]
         [1913 Webster]

   Slough grass (Bot.), a name in the Mississippi valley for
      grasses of the genus Muhlenbergia; -- called also drop
      seed, and nimble Will.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Nimble \Nim"ble\ (n[i^]m"b'l), a. [Compar. Nimbler
   (n[i^]m"bl[~e]r); superl. Nimblest (n[i^]m"bl[e^]st).] [OE.
   nimel, prob. orig., quick at seizing, fr. nimen to take, AS.
   niman; akin to D. nemen, G. nehmen, OHG. neman, Icel. nema,
   Goth. nima, and prob. to Gr. ne`mein to distribute. [root] 7.
   Cf. Nomand, Numb.]
   Light and quick in motion; moving with ease and celerity;
   lively; swift.
   [1913 Webster]

         Through the mid seas the nimble pinnace sails. --Pope.
   [1913 Webster]

   Note: Nimble is sometimes used in the formation of
         self-explaining compounds; as, nimble-footed,
         nimble-pinioned, nimble-winged, etc.
         [1913 Webster]

   Nimble Will (Bot.), a slender, branching, American grass
      (Muhlenbergia diffusa), of some repute for grazing
      purposes in the Mississippi valley.
      [1913 Webster]

   Syn: Agile; quick; active; brisk; lively; prompt.
        [1913 Webster]

WordNet (r) 3.0 (2006):

nimble Will
    n 1: slender branching American grass of some value for grazing
         in central United States [syn: nimblewill, nimble Will,
         Muhlenbergia schreberi]