adv. 意外地,偶然地
拆分：ac-加强意义 + -cid-降临 + -ent名词词尾 + -al形容词词尾,…的 + -ly副词词尾,方式/程度
例：As I turned around, I accidentally hit him in the face. 我转身时不经意撞了他的脸。She gave the answer away accidentally. 她无意中泄露了答案。
