chub (n.)

"fat, round, and plump," 1610s, literally "resembling a chub," from chub, the short, thick type of fish + -y (2). Perhaps influenced by Old Norse kumba "log," kumben "stumpy."

ME chubbe ... was also used of a "lazy, spiritless fellow; a rustic, simpleton; dolt, fool" (1558), whilst Bailey has "Chub, a Jolt-head, a great-headed, full-cheeked Fellow," a description reminiscent of that of the chevin, another name for the chub ... Thus the nickname may have meant either "short and thick, dumpy like a chub," or "of the nature of a chub, dull and clownish." ["Dictionary of English Surnames"]

1703, "short, thick lump of wood," of uncertain origin, perhaps a variant of chunk (n.) or a nasalized variant of chub (compare chuck/chunk and Old Norse kumbr for kubbr "block of wood"). Meaning "blockhead" is first attested 1883. Chump change attested by 1950.