Obsolete words slightly altered, and made current again- as “chestnut” for castnut, from Castana, in Thessaly; “court-cards” for coat-cards; “currants” for corinths; “frontispiece” for frontispice (Latin frontispicium); “Isinglass” for hausen blase (the sturgeon's bladder, Ger.); “shame-faced” for shamefast, as steadfast, etc.; “sweetheart” for sweethard, as drunkard, dullard, dotard, niggard.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Metamorphic Words from Infoplease: