1784, "man with an alto voice," literally "high," from Italian alto (canto), from Latin altus "high," literally "grown tall," from PIE root *al- (2) "to grow, nourish." Originally a man's high voice; now more commonly applied to the lower range of women's voices (which is more strictly the contralto), an extension recorded by 1848. So called because higher than the tenor, which in old music had the melody.
The alto in a man is totally distinct from the contralto in a woman. The tone is utterly different -- the best notes of the one are certainly not the best notes of the other; and although in certain cases a contralto may sing with good effect music written for a male alto (e.g. in some oratorios), yet the converse is scarcely ever true. ["How to Sing," 1890]
As a type of saxophone, from 1869. Also an old name for the viola (1833), from Italian.