1. (Music, other)

a. the arrangement of the relative durations of and accents on the notes of a melody, usually laid out into regular groups (bars)of beats, the first beat of each bar carrying the stress
b. any specific arrangement of such groupings; time: quadruple rhythm.
2. (Poetry) (in poetry)

a. the arrangement of words into a more or less regular sequence of stressed and unstressed or long and short syllables
b. any specific such arrangement; metre
3. (Art Terms) (in painting, sculpture, architecture, etc) a harmonious sequence or pattern of masses alternating with voids, of lightalternating with shade, of alternating colours, etc
4. (Physiology) any sequence of regularly recurring functions or events, such as the regular recurrence of certain physiological functions of the body, as the cardiac rhythm of the heartbeat