An Etymological Dictionary of the German Language/Annotated/kostspielig

by Friedrich Kluge

kostspielig, adjective, ‘expensive,’ first used towards the end of the 18th century; it contains, however, an old word which has elsewhere disappeared, and even in this compound has been corrupted; Middle High German spildec, ‘extravagant’; Old High German spilden, ‘to squander, dissipate’ (from Old High German gaspilden, French gaspiller is derived). Hence *kostspildig is probably ‘squandering money’; spildig, which was etymologically obscure, was corrupted into -spielig.