The Collaborative International Dictionary of English v.0.48:

Trough \Trough\ (tr[o^]f), n. [OE. trough, trogh, AS. trog,
   troh; akin to D., G., & Icel. trog, Sw. tr[*a]g, Dan. trug;
   probably originally meaning, made of wood, and akin to E.
   tree. [root]63 & 241. See Tree, and cf. Trug.]
   1. A long, hollow vessel, generally for holding water or
      other liquid, especially one formed by excavating a log
      longitudinally on one side; a long tray; also, a wooden
      channel for conveying water, as to a mill wheel.
      [1913 Webster]

   2. Any channel, receptacle, or depression, of a long and
      narrow shape; as, trough between two ridges, etc.
      [1913 Webster]

   3. (Meteor.) The transverse section of a cyclonic area where
      the barometric pressure, neither rising nor falling, has
      reached its lowest point.
      [Webster 1913 Suppl.]

   Trough gutter (Arch.), a rectangular or V-shaped gutter,
      usually hung below the eaves of a house.

   Trough of the sea, the depression between two waves.
      [1913 Webster]

WordNet (r) 3.0 (2006):

trough
    n 1: a narrow depression (as in the earth or between ocean waves
         or in the ocean bed)
    2: a channel along the eaves or on the roof; collects and
       carries away rainwater [syn: gutter, trough]
    3: a concave shape with an open top [syn: bowl, trough]
    4: a treasury for government funds [syn: public treasury,
       trough, till]
    5: a long narrow shallow receptacle
    6: a container (usually in a barn or stable) from which cattle
       or horses feed [syn: manger, trough]