∙ Pertaining to the revolution of a celestial object in its orbit. astronomy
∙ For which any return to it must occur in multiples of k{\displaystyle k} time steps, for some k>1{\displaystyle k>1}. mathematics, stochastic processes, of a state
∙ Having a structure characterized by periodic sentences. rhetoric
∙ Relating to, derived from, or designating, the highest oxygen acid (HIO) of iodine. chemistry