Odd one out

Four words, three that share something and one that does not. It is played two ways: by word class and — the one that really costs — by gender, which French predicts from nothing at all. Voiture is feminine and car is neuter in English, so there is nothing to carry over; livre is masculine and means book, but la livre, with the feminine article, is the pound. The four come without their article, because with le and la in front there would be nothing to play, and from the same level, because if the odd one were always the rarest word you could win by pointing at the one that looks unfamiliar.