The Collaborative International Dictionary of English v.0.48:

heavyweight \heavyweight\ adj.
   heaviest in a category; as, a heavyweight boxer.
   [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

heavyweight \heavyweight\ n.
   1. a wrestler who weighs more than 214 pounds.
      [WordNet 1.5]

   2. a boxer who weighs more than 195 pounds.
      [WordNet 1.5]

   3. a very large person.

   Syn: giant, hulk.
        [WordNet 1.5]

   4. a person of exceptional importance and reputation.

   Syn: colossus, behemoth, giant, titan.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

heavyweight
    n 1: an amateur boxer who weighs no more than 201 pounds
    2: a wrestler who weighs more than 214 pounds
    3: a professional boxer who weighs more than 190 pounds
    4: a very large person; impressive in size or qualities [syn:
       giant, hulk, heavyweight, whale]
    5: a person of exceptional importance and reputation [syn:
       colossus, behemoth, giant, heavyweight, titan]

Moby Thesaurus II by Grady Ward, 1.0:

105 Moby Thesaurus words for "heavyweight":
   Chinese boxer, Rasputin, Svengali, VIP, access, bad influence,
   bantamweight, big, big boy, big cheese, big wheel, big-league,
   big-name, big-time, big-timer, bigwig, bigwigged, black belt,
   blimp, boxer, brown belt, bruiser, catchweight, chief,
   consequential, considerable, court, double-barreled, earthshaking,
   eminence grise, fat, fat cat, fatty, featherweight, fighter,
   fisticuffer, five-percenter, flyweight, friend at court,
   good influence, grand, gray eminence, great, heavy, hefty,
   hidden hand, high-powered, hippo, important, influence,
   influence peddler, influencer, ingroup, karate expert, key,
   kingmaker, leaden, leader, light heavyweight, lightweight, lion,
   lobby, lobbyist, lords of creation, lump, major, man of influence,
   manipulator, massive, massy, material, middleweight, momentous,
   name, open sesame, overweight, palooka, ponderous, potbelly,
   powers that be, pressure group, prizefighter, pug, pugilist,
   roly-poly, savate expert, self-important, significant,
   sinister influence, sparrer, special interests,
   special-interest group, substantial, superior, swagbelly,
   the Establishment, tub, tub of lard, tun, very important person,
   weighty, welterweight, wheeler-dealer, wire-puller,
   world-shaking



The Jargon File (version 4.4.7, 29 Dec 2003):

heavyweight
 adj.

    [common] High-overhead; baroque; code-intensive; featureful, but costly.
    Esp. used of communication protocols, language designs, and any sort of
    implementation in which maximum generality and/or ease of implementation
    has been pushed at the expense of mundane considerations such as speed,
    memory utilization, and startup time. EMACS is a heavyweight editor; X
    is an extremely heavyweight window system. This term isn't pejorative, but
    one hacker's heavyweight is another's elephantine and a third's 
    monstrosity. Oppose lightweight. Usage: now borders on techspeak,
    especially in the compound heavyweight process.


The Free On-line Dictionary of Computing (30 December 2018):

heavyweight

   High-overhead; baroque; code-intensive; featureful, but
   costly.  Especially used of communication protocols, language
   designs, and any sort of implementation in which maximum
   generality and/or ease of implementation has been pushed at
   the expense of mundane considerations such as speed, memory
   use and startup time.  Emacs is a heavyweight editor; X is
   an *extremely* heavyweight window system.  This term isn't
   pejorative, but one hacker's heavyweight is another's
   elephantine and a third's monstrosity.

   Opposite: "lightweight".  Usage: now borders on technical
   especially in the compound "heavyweight process".

   (1994-12-22)