aria

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A solo vocal piece with instrumental accompaniment, as in an opera.
• noun An air; a melody.

from The Century Dictionary.

• noun Special varieties of movement or style are indicated by adding various terms: as, aria cantabile, an aria in a flowing, connected style, with but slight accompaniment; aria concertato, an aria of large dimensions, with an elaborate or concerted accompaniment; aria parlante, an aria in which the dramatic delivery of the text is conspicuous; aria di bravura or d'agilita, an aria in which special opportunity is given for vocal display through rapid passages and figures, trills and other embellishments, extreme notes, and the like; aria d'imitazione, an aria in which the music recalls some physical sound like the song of birds, the noises of battle, etc.
• noun In music: A rhythmical and metrical melody or tune for a single voice (rarely for a monophonous instrument), having a vocal or instrumental accompaniment: distinguished from a song by being less simple and less purely lyrical. The aria grande is the next most elaborate species of solo vocal music to the scena (which see).
• noun A distinct form of solo vocal music, distinguished by a clear division into three parts, namely, a principal section, a subordinate section, and a repetition, with or without alterations, of the first section: otherwise known as the da capo form.
• noun A solo movement, whether in strict aria form or not, in an extended vocal work, like an opera or an oratorio: as, the soprano aria “I know that my Redeemer liveth.”

from the GNU version of the Collaborative International Dictionary of English.

• noun (Mus.) An air or song; a melody; a tune.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A musical piece written typically for a solo voice with orchestral accompaniment in an opera or cantata.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an elaborate song for solo voice