The Collaborative International Dictionary of English v.0.48:

Tuba \Tu"ba\, n. [L., trumpet.] (Mus.)
   (a) An ancient trumpet.
   (b) A sax-tuba. See Sax-tuba.
       [1913 Webster]

WordNet (r) 3.0 (2006):

tuba
    n 1: the lowest brass wind instrument [syn: bass horn,
         sousaphone, tuba]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "tuba":
   alpenhorn, alphorn, althorn, alto horn, ballad horn, baritone,
   bass horn, brass choir, brass wind, brass-wind instrument, brasses,
   bugle, bugle horn, clarion, cornet, cornet-a-pistons,
   corno di caccia, cornopean, double-bell euphonium, euphonium,
   helicon, horn, hunting horn, key trumpet, lituus, lur, mellophone,
   ophicleide, orchestral horn, pocket trumpet, post horn, sackbut,
   saxhorn, saxtuba, serpent, slide trombone, sliphorn, sousaphone,
   tenor tuba, tromba, trombone, trumpet, valve trombone,
   valve trumpet



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

TUBA
       TCP and UDP with Bigger Addresses (TCP, UDP, RFC 1347)


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

TUBA

    An Internet protocol, described in
   RFC 1347, RFC 1526 and RFC 1561, and based on the OSI
   Connectionless Network Protocol (CNLP).

   TUBA is one of the proposals for Internet Protocol Version
   6.

   (1995-04-03)