I. noun 1. (especially in church music) the highest adult male singing voice (sometimes distinguished from the countertenor voice as using falsetto). 2. the lowest female singing voice; contralto. 3. a person with an alto voice. 4. a part written for an alto voice. 5. [as modifier] — denoting the member of a family of instruments pitched second or third highest • alto flute.
6. an alto saxophone. II. derivatives altoist noun
– origin late 16th cent.: from Italian alto (canto) ‘high (song)’.