firstlyadv.
英 'fɜːs(t)lɪ | 美 'fɝstli
中文adv. 首先（主要用于列举条目、论点时）；第一
词根词源
firstly (adv.)"in the first place, before anything else," 1530s, but never a common word (simple first usually serving its place), from first + -ly (2).
关键词