A colonist is a person who goes to live in a new colony. A colony is a place that another country has started far from home, and the colonist is one of the people who settle there — they stay, build a house, farm the land, and try to make a new life. In school history you meet colonists leaving Britain for North America, or Spain for Latin America, and so on. The word sounds calm and factual, like a job title. Though actually, for the people who already lived on that land, colonists were often not welcome guests; they were taking the land. So the word can feel clean in a textbook and much heavier in real life. Settler is a close everyday cousin; colonist is a little more formal and more tied to the idea of a colony. You would not call someone who moves to Taipei for work a colonist. The move has to be part of that colony story.