chump

The word 'chump' emerged in British English during the 18th century. Its exact origin is uncertain, but it is widely considered an expressive or onomatopoeic coinage, perhaps meant to evoke the dull, thick sound of chopping wood or the sense of a heavy, solid block. This concrete, physical sense of a 'block of wood' or 'short, thick piece' evolved metaphorically by the late 19th century to describe a person perceived as dull-witted or blockheaded. The semantic journey thus moved from a literal, lumpish object to a figurative label for a foolish individual, a common pattern in English slang.

The word is a simplex. It is likely an expressive formation, possibly imitative of the sound of a dull blow or a heavy, lumpish object.