Once in a while means not often, but sometimes. Once in a while we treat ourselves.
It is warmer than every now and then and usually introduces something pleasant. Every once in a while is the fuller American form.
1phraseonce in a whileNot often, but sometimes.
“Once in a while they drive out to the coast for the day.”
once in a while is a phrase.
Practised in Small Talk & Everyday Phrases