We called in the plumber because of the periodic hammering in the pipes. The next periodic return of Halley's comet is expected in 2061-62.
Advanced English Dictionary
+adjective [usually before noun] happening fairly often and regularly: Periodic checks are carried out on the equipment. + He makes periodic visits to all the shops which stock his products. periodically adverb: Mailing lists are updated periodically. + Periodically, we meet to discuss any problems.
Random quote: If you'll not settle for anything less than your best, you will be amazed at what you can accomplish in your lives.: Vince Lombardi