A colonialist is a person who wants, supports, or takes part in colonialism — the idea that one country should rule another as a colony. It can also be an adjective: a colonialist policy, a colonialist way of thinking. This word is not the same as colonist. A colonist is someone who goes to live in a colony. A colonialist is about the belief or the ruling system. One person can be both, but the words pick out different things, and it is kind to keep them apart. In modern English, colonialist is usually not a compliment. It is a critical, political word. You will see it in newspapers and school writing more than in everyday chat. If you only need “a person who settled there,” colonist is the quieter, more historical word. If you are talking about the idea of ruling other lands, colonialist is the one that carries the judgment.