once in a blue moon, Somethingthathappensveryrarely.
over the moon, Extremelyhappyorpleased.
Word Origin
Language
Old English
Original word
mōna
Originally meant
The natural satellite of the Earth
Background
The word 'moon' comes from the Old English 'mōna', which is related to the Germanic and Norse words for the moon. It has been used to describe Earth's natural satellite for centuries.