1784, "man with an alto voice," from Italian alto (canto), from Latin altus "high" (see old). Originally a "high" man's voice, now more commonly applied to the lower range of women's voices (which is more strictly the contralto), an extension first recorded in 1881.
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.