baritone (n.)

c. 1600, "male voice between tenor and bass," from Italian baritono, from Greek barytonos "deep-toned, deep-sounding," from barys "heavy, deep," also, of sound, "strong, deep, bass" (from PIE root *gwere- (1) "heavy") + tonos "tone," from PIE root *ten- "to stretch."

Technically, "ranging from lower A in bass clef to lower F in treble clef." Meaning "singer having a baritone voice" is from 1821. As a type of brass band instrument, it is attested from 1949. As an adjective, 1729 in reference to the voice, 1854 of musical instruments (originally the concertina).

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Definitions of baritone from WordNet
baritone (n.)
a male singer;
Synonyms: barytone
baritone (n.)
the second lowest adult male singing voice;
Synonyms: baritone voice
baritone (n.)
the second lowest brass wind instrument;
Synonyms: baritone horn
baritone (adj.)
lower in range than tenor and higher than bass;
baritone oboe
a baritone voice