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]

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

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)