1.Definition: occurring from time to time

"Took an occasional glass of wine"

2.Definition: occurring on a temporary or irregular basis

"An occasional worker"

Related Adjective(s):casual

3.Definition: occurring or appearing at usually irregular intervals

"Occasional headaches"

Related Adjective(s):episodic

4.Definition: recurring or reappearing from time to time

Related Adjective(s):periodic