Sporadic (adjective)

1. Occurring at irregular intervals; not constant or steady.
2. Scattered or occurring in scattered or isolated instances.

Origin:

From the latin word sporadicus, from greek spōradikos "scattered, dispersed", from spōros "seed, sowing".

Examples:

1. The sporadic outbreaks of violence are causing concern among local residents.
2. He had a sporadic work history, with long periods of unemployment.
3. The sporadic rain showers throughout the day made it difficult to schedule outdoor activities.
4. Sporadic attendance caused the class to be less cohesive.
5. The sporadic power outages were causing frustration for local businesses.