From these clues, I deduced that the keys might be lost in the park.

deduced 是动词 deduce 的过去式。deduce 由前缀 de-（表示"向下、去除"）和词根 duce（来自拉丁语 ducere，意为"引导"）组成，字面意思是"向下引导"，引申为"通过逻辑推理得出结论"，即"推断、演绎"。