"melody for a single voice," from Italian aria, literally "air" (see air (n.1)).
Historically considered, the aria marks a single moment in the course of a dramatic action. The text often consists of but a few words, many times repeated (as we find in Handel's oratorios, etc.), and the musical development is the main thing. The opposite of aria is recitative (q.v.), in which the declamation of the syllables is the main thing, colored, perhaps, by means of clever orchestration. [W.S.B. Mathews and Emil Liebling, "Dictionary of Music," 1896]