His callousness towards others' suffering was shocking.

callousness 是由形容词 callous（麻木不仁的）加上名词后缀 -ness 构成的名词。callous 本意是"硬结的、起老茧的"，引申为"麻木不仁的、无情的"。 callousness 指"麻木不仁、冷酷无情"的状态或品质。