Source : Webster's Revised Unabridged Dictionary (1913)

Shelf \Shelf\, n.; pl. {Shelves}. [OE. shelfe, schelfe, AS.
   scylfe; akin to G. schelfe, Icel. skj[=a]lf. In senses 2 & 3,
   perhaps a different word (cf. {Shelve}, v. i.).]
   1. (Arch.) A flat tablet or ledge of any material set
      horizontally at a distance from the floor, to hold objects
      of use or ornament.

   2. A sand bank in the sea, or a rock, or ledge of rocks,
      rendering the water shallow, and dangerous to ships.

            On the tawny sands and shelves.       --Milton.

            On the secret shelves with fury cast. --Dryden.

   3. (Mining) A stratum lying in a very even manner; a flat,
      projecting layer of rock.

   4. (Naut.) A piece of timber running the whole length of a
      vessel inside the timberheads. --D. Kemp.

   {To lay on the shelf}, to lay aside as unnecessary or
      useless; to dismiss; to discard.

Source : WordNet®

shelf
     n 1: a support that consists of a horizontal surface for holding
          objects
     2: a projecting ridge on a mountain or submerged under water
        [syn: {ledge}]
     [also: {shelves} (pl)]

Source : Free On-Line Dictionary of Computing

shelf
     
        A public library of {class}es for the {Eiffel} language.