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