He diffidently offered his suggestion.

diffidently 是副词，由形容词 diffident 加后缀 -ly 构成。diffident 来自拉丁语 diffidere（不信任），由前缀 dis-（表示"不"）和 fidere（信任）组成，意思是"缺乏自信的、羞怯的"。diffidently 表示"胆怯地、缺乏自信地"。