Chubby
early 17th century (in the sense ‘short and thickset, like a chub’): from chub.
wiktionary
Recorded since 1611, from chub(“short, thick fish species used as bait"; used metaphorically since 1558 for "lazy person”), an assibilated form of cub(“a lump, heap, mass”) and cob, from Middle English *cubbe (found only in derivative cubbel(“a block to which an animal is tethered”)), from Old Norse kubbr, kumbr(“block, stump, log”) and/or Old Norse kumben(“stumpy”), equivalent to chub + -y. Cognate with dialectal Swedish kubbug(“fat, plump, chubby”). More at chub.
etymonline
chubby (adj.)
"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"]
