A bigamist is a person who is married to two people at the same time. In most countries that is a crime: the law says you must end one marriage before you start another. The word names the person, not the crime itself — the crime is bigamy. People use it in news and in court, not in chat about everyday life. Though actually it is not the same as polygamy. Polygamy is a marriage system some groups still practise in the open, with more than one spouse allowed. A bigamist is usually someone who marries again while the first marriage is still legal, often without the other person knowing.