Once in a blue moon

اتفاق یا فرصت خیلی نادر. بعد از مدتهای مدید. خیلی به ندرت.

The earthquakes hits once in a blue moon in this part of the earth, we never felt it.

I don’t know why she bought that music system – she uses it once in a blue moon.

“I think my grandson doesn’t love me anymore, he comes to see me only once in a blue moon.”