He suddenly interjected his opinion when the discussion became heated.

interjected 是动词 interject 的过去式。interject 由前缀 inter-（表示"在...之间"）和动词 ject（源自拉丁语 jacere，意为"投掷"）组成，字面意思是"在谈话过程中投掷进去"，引申为"突然插入（话语）"。