We were expecting thirty people to come, but half of them never showed up.

showed 是动词 show 的过去式，show 的基本意思是"展示、显示"。 up 是副词，常与动词搭配表示"出现、到场"或"完成"的意思。 showed up 这个短语动词表示"出现、到场"，特别是指按约定或预期出现。