During the discussion, he suddenly deviated from the topic and started talking about the weather.

deviated 是动词 deviate 的过去式。deviate 由前缀 de-（表示"离开"）和词根 via（拉丁语"道路"）组成，字面意思是"离开道路"，引申为"偏离、背离"。 在句中表示从讨论主题突然转向其他话题的行为。