[Which Word] ※ firstly / first of all / at first • Firstly and first (of all) are used to introduce a series of facts, reasons, opinions, etc: e.g.) The brochure is divided into two sections, dealing firstly with basic courses and secondly with advanced ones. • Firstly is more common in British English than in North American English. • At first is used to talk about the situation at the beginnin..