In law, a punishable act is one the law can punish. If something is punishable, you can be fined, sent to prison, or given another official penalty for doing it. You often hear it in the pattern punishable by…: 'punishable by a fine', 'punishable by up to two years in prison'. It is a formal, legal-sounding adjective, not a word for everyday family talk — a parent who says a child will lose phone time is not using punishable. Though actually, punishable does not tell you how bad the act is, only that the law has a penalty ready. A small offence and a serious crime can both be punishable; the next words (by a fine, by prison) do the real work. It describes the act, not the person: the crime is punishable, not 'he is punishable' in careful legal English, though you will hear looser talk.