The Collaborative International Dictionary of English v.0.48:

Skeleton \Skel"e*ton\, a.
   Consisting of, or resembling, a skeleton; consisting merely
   of the framework or outlines; having only certain leading
   features of anything; as, a skeleton sermon; a skeleton
   crystal.
   [1913 Webster]

   Skeleton bill, a bill or draft made out in blank as to the
      amount or payee, but signed by the acceptor. [Eng.]

   Skeleton key, a key with nearly the whole substance of the
      web filed away, to adapt it to avoid the wards of a lock;
      a master key; -- used for opening locks to which it has
      not been especially fitted.

   Skeleton leaf, a leaf from which the pulpy part has been
      removed by chemical means, the fibrous part alone
      remaining.

   Skeleton proof, a proof of a print or engraving, with the
      inscription outlined in hair strokes only, such proofs
      being taken before the engraving is finished.

   Skeleton regiment, a regiment which has its complement of
      officers, but in which there are few enlisted men.

   Skeleton shrimp (Zool.), a small crustacean of the genus
      Caprella. See Illust. under Laemodipoda.
      [1913 Webster]

WordNet (r) 3.0 (2006):

skeleton key
    n 1: a passkey with much of the bit filed away so that it can
         open different locks