The Collaborative International Dictionary of English v.0.48:

Chubby \Chub"by\, a.
   Like a chub; plump, short, and thick. "Chubby faces." --I.
   Taylor.
   [1913 Webster]

WordNet (r) 3.0 (2006):

chubby
    adj 1: sufficiently fat so as to have a pleasing fullness of
           figure; "a chubby child"; "pleasingly plump"; [syn:
           chubby, embonpoint, plump]

Moby Thesaurus II by Grady Ward, 1.0:

63 Moby Thesaurus words for "chubby":
   adipose, ample, beefy, big-bellied, bloated, blocky, blowzy,
   bosomy, brawny, burly, buxom, chunky, corpulent, distended, dumpy,
   fat, fattish, fleshy, full, gross, heavy, heavyset, hefty, hippy,
   imposing, lusty, meaty, obese, overweight, paunchy, plump, podgy,
   portly, potbellied, pudgy, puffy, pug, pugged, pursy, retrousse,
   roly-poly, rotund, round, roundabout, snub-nosed, square, squat,
   squattish, squatty, stalwart, stocky, stout, strapping, stubbed,
   stubby, stumpy, swollen, thick-bodied, thickset, top-heavy, tubby,
   turned-up, well-fed