Changeling

1. a. Given to change; inconstant.
2. n. One who, or that which, is left or taken in the place of another, as a child exchanged by fairies.
3. n. A simpleton; an idiot.
4. n. One apt to change; a waverer.
5. a. Taken or left in place of another; changed.

The word meanings were obtained from OPTED(The Online Plain Text English Dictionary), which is based on “The Project Gutenberg Etext of Webster’s Unabridged Dictionary” which is in turn based on the 1913 US Webster’s Unabridged Dictionary (See Project Gutenburg), as a text file.