From WordNet (r) 3.0 (2006) [wn]:
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, shelf]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
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.
[1913 Webster]
2. A sand bank in the sea, or a rock, or ledge of rocks,
rendering the water shallow, and dangerous to ships.
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On the tawny sands and shelves. --Milton.
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On the secret shelves with fury cast. --Dryden.
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3. (Mining) A stratum lying in a very even manner; a flat,
projecting layer of rock.
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4. (Naut.) A piece of timber running the whole length of a
vessel inside the timberheads. --D. Kemp.
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To lay on the shelf, to lay aside as unnecessary or
useless; to dismiss; to discard.
[1913 Webster]
From The Free On-line Dictionary of Computing (8 July 2008) [foldoc]:
shelf
A public library of classes for the Eiffel language.