A pederast is a man who has sex with a boy. In today's English this is a very serious word. It names a crime and a kind of harm, not a joke and not a light insult. You will see it in news, law, and history books. You will not hear it much in kind everyday talk, and you should not throw it at someone in a fight. Though actually, older writing about ancient Greece uses this family of words for a custom of that time, where an adult man had a sexual relationship with a teenage boy. That is history, and scholars still argue about how to talk about it. It does not make the modern meaning softer. In the world we live in now, a man having sex with a boy is against the law and deeply wrong. People sometimes reach for 'pedophile' as a wider word (sexual interest in children). Pederast is narrower: a man, and a boy.

與男童發生性關係的男人（台灣常籠統說「戀童癖」，但此字更窄）