The Collaborative International Dictionary of English v.0.48:

tux \tux\
   Shortened form of tuxedo. [informal]
   [PJC] Tuxedo

WordNet (r) 3.0 (2006):

tux
    n 1: semiformal evening dress for men [syn: dinner jacket,
         tux, tuxedo, black tie]

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

TUX
       Torvalds UniX (Linux), "Tux"


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

Tux


    Tux the Penguin is the official emblem of Linux, This eventuated after a
    logo contest in 1996, during which Linus Torvalds endorsed the idea of a
    penguin logo in a couple of famously funny postings. Linus explained that
    he was once bitten by a killer penguin in Australia and has felt a special
    affinity for the species ever since. (Linus has since admitted that he was
    also thinking of Feathers McGraw, the evil-genius penguin jewel thief who
    appeared in a Wallace & Grommit feature cartoon, The Wrong Trousers.)

    Larry Ewing designed the official Tux logo. It has proved a wise choice,
    amenable to hundreds of recognizable variations used as emblems of
    Linux-related projects, products, and user groups. In fact, Tux has spawned
    an entire mythology, of which the Gospel According to Tux and the mock-epic
    poem Tuxowolf are among the best-known examples.

    There is a ?real? Tux ? a black-footed penguin resident at the Bristol Zoo.
    Several friends of Linux bought a zoo sponsorship for Linus as a birthday
    present in 1996.