changeling

Etymology

The noun is derived from change + -ling (suffix with the sense ‘immature; small’). Sense 6 (“idiot, simpleton”) is from the idea that foolish children had been left by magical creatures (sense 1). The adjective is derived from the noun.

noun

1. (European folklore, also figurative) In pre-modern European folklore: an infant of a magical creature that was secretly exchanged for a human infant. In British, Irish and Scandinavian mythology the exchanged infants were thought to be those of fairies, sprites or trolls; in other places, they were ascribed to demons, devils, or witches.
   Juſt as a Changeling ſeems below the reſt / Of Men, or rather is a two-legg’d Beaſt, / So theſe Gigantick Souls amaz'd we find / As much above the reſt of human kind. 1709, Earl of Murlgrave [i.e., John Sheffield, 1st Duke of Buckingham and Normanby, formerly Earl of Mulgrave], An Essay on Poetry, London: […] H. Hills,[…], →OCLC, page 15
   It was easy enough to see that the child was a changeling, for it wasn't like other children at all it screamed and cried, as if a knife stuck in it, and it wheezed and hit about with its arms like a huldre-cat, and was as ugly as sin. 1886, Peter Christen Asbjørnsen, translated by H.L. Brækstad, Folk and Fairy Tales, page 298
   His nurse had told him all about changelings, and how the little people would always try to steal a beautiful human child out of its cradle and put in its stead one of their own ailing, puking brats … 1961, Muriel Saint Clare Byrne, Elizabethan Life in Town and Country, 8th edition, London: Methuen & Co., →OCLC, page 285
2. (by extension) A person or object (especially when regarded as inferior) secretly exchanged for something else.
   When I firſt read Mr. Walker’s Circular Letter to the Arch-deacons, I fancied he intended to give us an Account of thoſe worthy Men, … But after about ten Years going with this Work, and that the Time of its Birth was come, I ſoon found it to be a perfect Changeling. Inſtead of what I expected it to be, I ſaw a huge Heap of the moſt Heterogeneous Characters, … a great many of them much more deſerving to have their Names blotted out, than their Memory to be preſerved. 1717, [John Lewis], A Few English Notes on a Late Sermon Preached before the Sons of the Clergy by Dr. [Thomas] Bisse, Intended to Vindicate the English Reformation from the Charge of Sacrilege, Fraud, &c.[…], London: […] James Knapton,[…]; and sold by John Morphew,[…], →OCLC, page 15
3. (by extension, informal, rare) An infant secretly exchanged with another infant deliberately or by mistake; a swapling.
4. (fantasy, science fiction) An organism which can change shape to mimic others; a shape-shifter.
5. (archaic, also figurative) A person apt to change their loyalty or thinking; a waverer.
   Fal[staff]. … If you will lodge with me in Eaſtcheap, you ſhall ſee the thouſand pound fairly ſpent in ſack: you ſhall ſhare with me to the utmoſt farthing. But for dry reſtitution, I have not been accustom'd to it of many years. You would not have me a changeling at this time of day, I hope, Maſter Shallow. / Shal[low]. Changeling! no, Sir John, thou art no changeling; but, depend on it, I will not put up with this wrong. … I will have my money; depend on't I will have my money. 1760, [William] Kenrick, Falstaff’s Wedding: A Comedy.[…], London: […] J. Wilkie, …, →OCLC, act II, scene vi, page 28
6. (obsolete) An idiot, a simpleton.
   They alſo obſerue Lunaticks and changelings, and the Coniurer writeth downe their ſayings in a booke, groueling on the ground, as if he whiſperd to the Deuill to tell him the truth, and ſo expoundeth the letter, as it were by inſpiration. 1622, John Rawlins, The Famovs and Wonderfvll Recoverie of a Ship of Bristoll, Called the Exchange, from the Turkish Pirates of Argier.[…], London: […] [Eliot’s Court Press] for Nathaniel Butter,[…], →OCLC
   [C]an there be any one Sort of Men that enjoy themſelves better than thoſe which we call Idiots, Changelings, Fools, and Naturals? It may perhaps ſound harſh, but upon due Conſideration it will be found abundantly true, that theſe Perſons in all Circumſtances fare beſt, and live moſt comfortably: … 1740, Erasmus, “A Panegyrick upon Folly, Declamation-wise”, in W. Kennet [i.e., White Kennett], transl., The Praise of Folly. Made English from the Latin of Erasmus.[…], 6th edition, London: […] R[obert] Dodsley,[…], →OCLC, page 59

adj

1. (archaic, rare) Changeable, fickle, inconstant, wavering.
   Away thou changeling motley humouriſt, / Leave me, and in this ſtanding wooden cheſt, / Conſorted with theſe few books, let me lye / In priſon, and here be coffin'd, when I dye. In Donne’s Poems (1st edition, 1633), page 325, the word fondling is used instead of changeling. 1719, John Donne, “Satyre I”, in Poems on Several Occasions.[…], London: […] Jacob Tonson, and sold by William Taylor[…], →OCLC, page 107