Sentence:  There was some laughter, and Roddle was left free to expand his ideas on the <WSD>periodic</WSD> visits of cowboys to the town. “Mason Rickets, he had ten big punkins a-sittin' in front of his store, an' them fellers from the Upside-down-F ranch shot 'em up […].” 
Meaning of the word marked with <WSD> tags:  Having repeated cycles.