Webster's Revised Unabridged Dictionary · 1913

Alto

Alto ({not transcribed}) , noun

[Italian alto high, from Latin altus. Compare Alt.]

1.
(Music) Formerly the part sung by the highest male, or counter-tenor, voices; now the part sung by the lowest female, or contralto, voices, between in tenor and soprano. In instrumental music it now signifies the tenor.
2.
An alto singer.
Collocations (1)
Alto clef (Music) , the counter-tenor clef, or the C clef, placed so that the two strokes include the middle line of the staff. — Moore