Her hair looked uncombed, as if she hadn't brushed it all day.

uncombed 是由前缀 un-（表示"不、非"）和动词 comb（梳理）的过去分词 combed 组合而成的形容词。comb 本意是"梳子"，作动词表示"用梳子梳理"。uncombed 字面意思是"未经梳理的"，形容头发凌乱的状态。