Many people searched for days after his sudden disappearance.

disappearance 是由动词 disappear（消失）加上名词后缀 -ance 构成的名词。disappear 本身由前缀 dis-（表示"否定、相反"）和 appear（出现）组成，字面意思是"不出现"。 disappearance 指"消失、失踪的状态或事实"。