sporadic

Từ điển WordNet v3.1 - WordNet Dictionary

adjective

recurring in scattered and irregular or unpredictable instances (Freq. 3)
- a city subjected to sporadic bombing raids
• Ant:
continual
• Similar to:
fitful, spasmodic, intermittent, periodic, occasional,
irregular, unpredictable, isolated, stray
• See Also:
discontinuous, noncontinuous, infrequent