recurrence (part of speech: noun)
regularity (part of speech: noun)
- For man- except those elect already named- is hardly aware of periodicity. - "Essays", Alice Meynell.
- The reason most probably depends, as before intimated, on another phenomenon of periodicity corresponding to the month. - "Moon Lore", Timothy Harley.
- " Periodicity," Steve said promptly. - "The Flying Stingaree", Harold Leland Goodwin.