Relier Pairs COMMON IDIOMS IN ENGLISHVersion en ligne A short list of common idioms in English. par kepa olaizola garcia 1 You can´t judge a book by its cover. 2 Costs an arm and a leg. 3 Break a leg. 4 Let the cat out of the bag. 5 Sleep on it. 6 When pigs fly. 7 Piece of cake. 8 Take it easy. 9 Hit the nail on the head. 10 Hit the books. Good luck. To think. To study. Relax Something that is precisely right. Something is very expensive. To disclose a secret that was supposed to be kept. Something is very easy. Something will never happen. You shouldn´t decide upon something based just on outward appearances.