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]

The Free On-line Dictionary of Computing (19 January 2023):

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)


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.