RHYTHM n. 4 definitions
In the widest sense, a dividing into short portions by a regular succession of motions, impulses, sounds, accents, etc., producing an agreeable effect, as in music poetry, the dance, or the like.
AIR n.
A musical idea, or motive, rhythmically developed in consecutive single tones, so as to form a symmetrical and balanced whole, which may be sung by a single voice to the stanzas of a hymn or song, or even to plain prose, or played upon an instrument; a melody; a tune; an aria.