once in a blue moon
/ˌwʌns ɪn ə ˌbluː ˈmuːn/
very rarely
once in a blue moon in a sentence
“He only visits once in a blue moon.”
Origin of once in a blue moon
From rare astronomical occurrence of second full moon in calendar month, appearing bluish
Related Words
piece of cake
something very easy to do
put all your eggs in one basket
to risk everything on a single venture
raining cats and dogs
raining very heavily
read between the lines
to understand the hidden meaning
spill the beans
to reveal secret information
take with a grain of salt
to view something with skepticism