idiom: an idiom is an expression, word, or phrase that means something different from what the words actually imply (e.g., dressed to kill means “well-dressed;” fly off the handle means “to become very angry;” used to means “formerly”).
There are literally thousands of idiomatic expressions in the English language. Here is a random list of some of the more popular ones. How many do you know?
the cold shoulder
take a knee
a fat cat
half-baked idea
cutthroat competition
dressed to kill
fly off the handle
cross my heart and hope to die
get the ax
a change of heart
have the world by the tail
put your money where your mouth is
save the day
sell someone short
tighten your belt