EUPHONIUM
euphonium
(noun) a bass horn (brass wind instrument) that is the tenor of the tuba family
Source: WordNet® 3.1
Etymology
Noun
euphonium (plural euphoniums)
(musical instruments) A valved brass instrument, a sax horn, the tenor of the tuba family of instruments, having the appearance very similar to that of a tuba. It is similar to and often used instead of a "Baritone" horn. (A true Baritone has a cylindrical tubing, while the Euphonium tubing is conical, though they both cover the same range of tones. This relationship is also between the Trumpet [cylindrical] and Cornet [conical] respectively.)
Source: Wiktionary
Eu*pho"ni*um, n. Etym: [NL. See Euphony.] (Mus.)
Definition: A bass instrument of the saxhorn family.
Source: Webster’s Unabridged Dictionary 1913 Edition