Traditionally, this ritual was believed to cleanse the soul of uncleanliness.

uncleanliness 是由形容词 unclean（不干净的）加上名词后缀 -ness 构成的名词，表示"不洁的状态"。unclean 本身由否定前缀 un-（表示"不"）和 clean（干净的）组成。