NOUN (3)

1. an amateur boxer who weighs no more than 126 pounds;

2. weighs 126-139 pounds;

3. a professional boxer who weighs between 123 and 126 pounds;

WordNet (r) 3.0 (2006):

featherweight
    n 1: an amateur boxer who weighs no more than 126 pounds
    2: weighs 126-139 pounds
    3: a professional boxer who weighs between 123 and 126 pounds

Moby Thesaurus II by Grady Ward, 1.0:

63 Moby Thesaurus words for "featherweight":
   Chinese boxer, bantam, bantamweight, banty, black belt, boxer,
   brown belt, bruiser, button, catchweight, chit, cluck, diminutive,
   dimwit, dumb, fighter, fingerling, fisticuffer, flyweight,
   forceless, heavyweight, imponderous, impotent, ineffective,
   ineffectual, inefficacious, karate expert, light heavyweight,
   lightweight, middleweight, mini, minikin, minnow, minny, mouse,
   no-account, nubbin, of no account, palooka, peewee, pony,
   powerless, prizefighter, pug, pugilist, runt, savate expert,
   shrimp, slip, small fry, snip, snippet, sparrer, tit,
   unauthoritative, underweight, unheavy, wart, weak, weightless,
   welterweight, wisp, without any weight