Definition of "periodic"

periodic¹

/ˌpɪɹiˈɒdɪk/

adjective
not comparable
1. Relative to a period or periods.
2. Having repeated cycles.
  Quotations
  There was some laughter, and Roddle was left free to expand his ideas on the periodic 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 […].”
  1899, Stephen Crane, chapter 1, in Twelve O'Clock
3. Occurring at regular intervals.
4. Periodical.
5. (astronomy) Pertaining to the revolution of a celestial object in its orbit.
6. (mathematics, stochastic processes, of a state) For which any return to it must occur in multiples of k time steps, for some k > 1 .
7. (rhetoric) Having a structure characterized by periodic sentences.

periodic²

/ˌpɜːɹaɪˈɒdɪk/

adjective
not comparable
1. Relating to the highest oxidation state of iodine; of or derived from a periodic acid.