Idioms
the idiom that means it's raining really hard
it's raining cats and dogs
the idiom that means don't judge someone or something by how it looks
don't judge a book by it's cover
the idiom that means something is really easy
it's a piece of cake
the idiom that means something doesn't happen very often
once in a blue moon
the idiom that means something is really expensive
it costs and arm and a leg