Happening or appearing at regular intervals
Happening or appearing now and then
"Time for our periodic chat, little brother," he said, and motioned to the other chair before the hearth.
Numerous attempts have been made to find periodic variations in thunderstorm frequency.
Instead they searched their surroundings wildly in the light of periodic lightning and the fire at the far end of the hall.
In its chemical relations, titanium is generally tetravalent, and occurs in the same sub-group of the periodic classification as zirconium, cerium and thorium.
His name is best known for the share he had in the periodic classification of the elements.