rhythm - noun

the basic rhythmic unit in a piece of music

recurring at regular intervals

an interval during which a recurring sequence of events occurs

the arrangement of spoken words alternating stressed and unstressed elements

natural family planning in which ovulation is assumed to occur 14 days before the onset of a period (the fertile period would be assumed to extend from day 10 through day 18 of her cycle)

rhythm - thesaurus

beat   cycle   round