“When they were little, John and his cousin were thick as thieves.” 「小さいころはジョンと従弟は泥棒みたいに仲が良かった。」
二人の人が「泥棒みたいに仲がいい」ということは、お互いの秘密を守る親友だという意味です。本当に泥棒というわけではありませんが、一緒に悪い事、いたずらをする可能性があります。一緒に犯罪を犯すペアみたいに協力し、お互いに忠誠です。
When two people are “thick as thieves”, they have a close relationship and keep each other’s secrets. They aren’t really thieves, although they might get into some mischief together. But they cooperate and work together just like partners in crime who are loyal to each other.
