Definition of periodic:
oscillating, infrequent, rhythmical, casual, cyclic, (every) now and then/again, recurring, pulsed, intermittent, sporadic, sometimes, periodical, isochronal, occasionally, occasional, every so often, oscillatory, from time to time, episodic, continue, repetition, spasmodic, fitful, rhythmic, repeated, on-and-off, study at intermittent, isochronous.
- recurrent (part of speech: adjective)
regular (part of speech: adjective)
- "The English Language", Robert Gordon Latham.
- "The Red Conspiracy", Joseph J. Mereto.
- "Community Civics and Rural Life", Arthur W. Dunn.