The Collaborative International Dictionary of English v.0.48:

Portly \Port"ly\, a. [From Port demeanor.]
   1. Having a dignified port or mien; of a noble appearance;
      imposing.
      [1913 Webster]

   2. Bulky; corpulent. "A portly personage." --Dickens.
      [1913 Webster]

WordNet (r) 3.0 (2006):

portly
    adj 1: euphemisms for `fat'; "men are portly and women are
           stout" [syn: portly, stout]

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "portly":
   adipose, beefy, big-bellied, bloated, blowzy, bosomy, brawny,
   burly, buxom, chubby, chunky, corpulent, distended, dumpy, fat,
   fattish, fleshy, full, gross, heavy, heavyset, hefty, hippy,
   imposing, lusty, meaty, obese, overblown, overweight, paunchy,
   plump, podgy, potbellied, pudgy, puffy, pursy, roly-poly, rotund,
   square, squat, squatty, stalwart, stocky, stout, strapping,
   swollen, thick-bodied, thickset, top-heavy, tubby, weighty,
   well-fed