Definify.com
Webster 1913 Edition
Alto
1.
(Mus.)
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.
Alto clef
(Mus.)
the counter-tenor clef, or the C clef, placed so that the two strokes include the middle line of the staff.
Moore.
Webster 1828 Edition
Alto
AL'TO.
[L. altus.] High.Alto and Basso, high and low, in old law, terms used to signify a submission of all differences of every kind to arbitration.