I was taken aback to discover that the word changeling does not mean at all what I thought it did, at least according to the dictionaries. The American Heritage Dictionary can stand in for all the rest, since they all have these three senses in one or another order: “1. A child secretly exchanged for another. 2. Archaic A changeable, fickle person. 3. Obsolete A person of deficient intelligence.” To my wife and me, it means something entirely different: in the words of Wiktionary, “An organism which can change shape to mimic others” (and believe me, I was glad to find that there, proving my wife and I were not completely bonkers). Does anybody know the history of that sense (which presumably the OED will document when it gets around to the C’s)? And which senses are you familiar with?