Their teamwork ended up defeating our proposal.

defeating 是动词 defeat 的现在分词形式。defeat 由前缀 de-（表示"向下、去除"）和词根 feat（来自拉丁语 facere，意为"做、完成"）组成，字面意思是"使...做不成"，引申为"击败、战胜"的意思。