Main entry: sporadic
Definition: recurring in scattered and irregular or unpredictable instances
Usage: a city subjected to sporadic bombing raids
Antonyms: continual
Definition: occurring without interruption; chiefly restricted to what recurs regularly or frequently in a prolonged and closely spaced series
Antonyms: regular
Definition: in accordance with fixed order or procedure or principle
Antonyms: regular
Definition: (of solids) having clear dimensions that can be measured; volume can be determined with a suitable geometric formula
Antonyms: regular
Definition: (used of the military) belonging to or engaged in by legitimate army forces
Antonyms: nonperiodic, aperiodic
Definition: not recurring at regular intervals
Antonyms: predictable
Definition: capable of being foretold