From Longman Dictionary of Contemporary English(every) once in a while(every) once in a whileSOMETIMESsometimes, although not often I do get a little anxious once in a while. I saw her in the shop every once in a while. → once
Examples from the Corpus
(every) once in a while• But look at them once in a while.• I do need to see every once in a while.• I used to take him out fishing once in a while.• They were both lonely, so why not see each other once in a while.• He just comes round once in a while and they go out.• I only see her every once in a while at school.• All of these Helen used, displayed, wore, not once in a while, but every day, blushing.• He calls me once in a while or I call him.• I think you should change your shampoo and conditioner once in a while to avoid product build-up. 