The Collaborative International Dictionary of English v.0.48:

Bunker \Bun"ker\, n. [Scot. bunker, bunkart, a bench, or low
   chest, serving for a seat. Cf. Bunk, Bank, Bench.]
   [1913 Webster]
   1. A sort of chest or box, as in a window, the lid of which
      serves for a seat. [Scot.] --Jamieson.
      [1913 Webster]

   2. A large bin or similar receptacle; as, a coal bunker.
      [1913 Webster]

   3. A small sand hole or pit, as on a golf course. [Scot.]
      --Sir W. Scott.
      [Webster 1913 Suppl.]

   4. (Golf) Hence, any rough hazardous ground on the links;
      also, an artificial hazard with built-up faces.
      [Webster 1913 Suppl.]

   5. (Mil.) A fortified position dug into the ground,
      especially one which is closed on top and has protective
      walls and roof, e. g. of reinforced concrete. For
      defending positions it usually has windows to view the
      surrounding terrain, but as a safe location for planning
      operations or storage, a bunker may be completely
      underground with no direct access to the surface.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Bunker \Bun"ker\, v. t. (Golf)
   To drive (the ball) into a bunker.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

bunker
    n 1: a hazard on a golf course [syn: bunker, sand trap,
         trap]
    2: a large container for storing fuel; "the ship's bunkers were
       full of coal"
    3: a fortification of earth; mostly or entirely below ground
       [syn: bunker, dugout]
    v 1: hit a golf ball into a bunker
    2: fill (a ship's bunker) with coal or oil
    3: transfer cargo from a ship to a warehouse