Common Italian idioms and what they actually mean

In Italian: Modi di dire

An idiom is where translating word by word stops working. In bocca al lupo is good luck, not a wolf's mouth. Non vedo l'ora means I can't wait, not I don't see the hour.

They are learned whole, as single blocks, because their parts cannot be swapped: it is in bocca al lupo, never in bocca alla lupa.

Knowing a few is what makes the difference between correct Italian and Italian that sounds native.