In Reply to: Skeleton key posted by Hanale on July 18, 2010 at 13:46:
: Why is a skeleton key so called? Possibilities are that it is a key which has been altered to a bare minimum in order to bypass the wards of a lock; or the shape of the keyholes for old lever type locks which resemble a skull; or it is a key which can unlock all locks in a house, even to the closet or cupboard containing the skeleton.
Skeleton to mean bones goes back to 1578. But skeleton meaning "bare outline" was not recorded until 1607 and "formed the basis of 'skeleton crew,' 'skeleton key.'" "The Barnhart Concise Dictionary of Etymology" by Robert K. Barnhart (HarperCollins Publishers, New York, 1995). Page 722.