The Collaborative International Dictionary of English v.0.48:

Gnu \Gnu\, n. [Hottentot gnu, or nju: cf. F. gnou.] (Zool.)
   One of two species of large South African antelopes of the
   genus Catoblephas, having a mane and bushy tail, and curved
   horns in both sexes. [Written also gnoo.]
   [1913 Webster]

   Note: The common gnu or wildebeest (Catoblephas gnu) is
         plain brown; the brindled gnu or blue wildebeest (C.
         gorgon) is larger, with transverse stripes of black on
         the neck and shoulders.
         [1913 Webster]

WordNet (r) 3.0 (2006):

gnu
    n 1: large African antelope having a head with horns like an ox
         and a long tufted tail [syn: gnu, wildebeest]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "gnu":
   Cape elk, Virginia deer, antelope, buck, camel, camelopard,
   caribou, deer, deerlet, doe, dromedary, eland, elk, fallow deer,
   fawn, gazelle, giraffe, hart, hartebeest, hind, kaama, moose,
   mule deer, musk deer, okapi, red deer, reindeer, roe, roe deer,
   roebuck, springbok, stag, wildebeest



V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

GNU
       GNU's Not Unix (recursive!, Unix, GNU, OS)


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

GNU
 /gnoo/, not, /noo/

    1. [acronym: ?GNU?s Not Unix!', see recursive acronym] A Unix-workalike
    development effort of the Free Software Foundation headed by Richard
    Stallman. GNU EMACS and the GNU C compiler, two tools designed for this
    project, have become very popular in hackerdom and elsewhere. The GNU
    project was designed partly to proselytize for RMS's position that
    information is community property and all software source should be shared.
    One of its slogans is ?Help stamp out software hoarding!? Though this
    remains controversial (because it implicitly denies any right of designers
    to own, assign, and sell the results of their labors), many hackers who
    disagree with RMS have nevertheless cooperated to produce large amounts of
    high-quality software for free redistribution under the Free Software
    Foundation's imprimatur. The GNU project has a web page at http://
    www.gnu.org/. See EMACS, copyleft, General Public Virus, Linux.

    2. Noted Unix hacker John Gilmore }, founder of Usenet's
    anarchic alt.* hierarchy.


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

GNU

    /g*noo/ 1. A recursive acronym:
   "GNU's Not Unix!".  The Free Software Foundation's project
   to provide a freely distributable replacement for Unix.  The
   GNU Manifesto was published in the March 1985 issue of
   Dr. Dobb's Journal but the GNU project started a year and a
   half earlier when Richard Stallman was trying to get funding
   to work on his freely distributable editor, Emacs.

   Emacs and the GNU C compiler, gcc, two tools designed
   for this project, have become very popular.  GNU software is
   available from many GNU archive sites.

   See also Hurd.

   2.  John Gilmore.

   [Jargon File]

   (1997-04-12)


The Devil's Dictionary (1881-1906):

GNU, n.  An animal of South Africa, which in its domesticated state
resembles a horse, a buffalo and a stag.  In its wild condition it is
something like a thunderbolt, an earthquake and a cyclone.

    A hunter from Kew caught a distant view
        Of a peacefully meditative gnu,
    And he said:  "I'll pursue, and my hands imbrue
        In its blood at a closer interview."
    But that beast did ensue and the hunter it threw
        O'er the top of a palm that adjacent grew;
    And he said as he flew:  "It is well I withdrew
        Ere, losing my temper, I wickedly slew
        That really meritorious gnu."
                                                           Jarn Leffer