euphōnion

Euphonium comes from Greek euphōnos (sweet-voiced, well-sounding), from eu (good, well) and phōnē (voice, sound). The instrument was developed by Ferdinand Sommer of Weimar in 1843, who coined the name euphonion for a conical-bore, valved brass instrument pitched in B-flat, one octave below the trumpet. Sommer chose the name because he considered its tone the most beautiful in the brass family. The name is aspirational. Whether the euphonium actually has the most beautiful brass sound is a matter of opinion. Sommer thought so.

The euphonium occupies the tenor-bass range of the brass family. It sounds an octave below the trumpet and an octave above the tuba. In military and concert bands, it plays the melodic line that the cello plays in the orchestra — singing above the bass, below the treble, carrying the emotional weight. The euphonium is sometimes called the 'cello of the band,' though euphonium players find this comparison patronizing.

The instrument is virtually unknown to the general public. Most people cannot identify a euphonium by sight or name. It looks like a small tuba. It sounds like a warm, dark trumpet. It appears in concert bands, brass bands, and military bands but almost never in orchestras, jazz clubs, or pop music. The euphonium is the best-kept secret in the brass family.

The word euphonium entered English from German musical vocabulary in the mid-19th century. The Greek root euphōnos also gives English 'euphony' (pleasing sound) and 'euphemism' (speaking well of something, i.e., substituting a mild word for a harsh one). The euphonium lives in good linguistic company.