Wiktionary
on an irregular basis
adv. (context idiomatic English) irregularly, occurring in irregular time intervals or patterns.
WordNet
on an irregular basis
adv. in an irregular manner; "her letters arrived irregularly" [syn: irregularly] [ant: regularly]
Usage examples of "on an irregular basis".
Subsequently they had fallen into the habit of eating there together on an irregular basis, never more than once a week and often no more than once every two or three weeks.
Adele Finaly has been my analyst for a half-dozen years, and I see her on an irregular basis.
She said the patrols are there on an irregular basis so as not to set up a pattern.