'Euphonium' definitions:

Definition of 'euphonium'

From: WordNet
noun
A bass horn (brass wind instrument) that is the tenor of the tuba family

Definition of 'Euphonium'

From: GCIDE
  • Euphonium \Eu*pho"ni*um\, n. [NL. See Euphony.] (Mus.) A bass instrument of the saxhorn family. [1913 Webster]