A brigadier is a high rank in the British army, and also the person who has that rank. A brigadier is usually in charge of a brigade — a large group of soldiers, often thousands of people, made of several smaller units. In the British system, brigadier sits above colonel and below major general. It is senior, but here is the messy bit: the United States does not really use brigadier on its own. Americans say brigadier general, and that person is a one-star general. In Britain a brigadier is not called a general, even though the job sits in about the same place. Students who learn from American films will expect a star and the word general; British usage is quieter. You write a small b when it is the rank in a sentence (“she was promoted to brigadier”), and a capital B in a title before a name (Brigadier Smith). It is formal military English. Ordinary people mainly meet it in army news, in history, and in stories.