1. Having or marked by repeated cycles.

2. Happening or appearing at regular intervals.

3. Recurring or reappearing from time to time; intermittent.

4. Characterized by periodic sentences. -pe1ri0od2i0cal0ly adv.

SYNONYMS: periodic, sporadic, intermittent, occasional, fitful. These adjectives all mean recurring or reappearing now and then. Something periodic occurs at regular or at least generally predictable intervals: periodic feelings of anxiety. Sporadic implies appearance or occurrence in scattered, irregular, unpredictable, or isolated instances: a city subjected to sporadic bombing raids. Intermittent describes something that stops and starts at intervals: intermittent rain showers. What is occasional happens at random and irregularly: occasional outbursts of temper. Something fitful occurs in spells and often abruptly: fitful bursts of energy.

USAGE NOTE: Periodic has long been used loosely to mean "occasional, intermittent," but this usage may be confusing for readers who are accustomed to using the word only in its narrower sense of "at regular or predictable intervals." Thus the writer who said Parker's losses at the track were not covered by his periodic winners invited the (most likely unintended) inference that Parker had a system that enabled him to pick winners at regular intervals. Substitution of occasional in this context would have resolved the ambiguity.

Adjective: Happening or appearing at regular intervals. recurrent, cyclic.

Adjective: Happening or appearing now and then. Occasional, sporadic, intermittent, fitful.