WordNet sense 1 (an interval during which a recurring sequence of events occurs):

cycle, round

WordNet sense 2 (the basic rhythmic unit in a piece of music):

beat, musical rhythm

WordNet sense 3 (the arrangement of spoken words alternating stressed and unstressed elements):

speech rhythm

WordNet sense 4 (recurring at regular intervals):

regular recurrence

WordNet sense 5 (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 method of birth control, calendar method, calendar method of birth control, rhythm method