Her callous reaction to his job loss was shocking.

callous 是形容词，由名词 callus（老茧、硬皮）加上形容词后缀 -ous 构成。callus 指皮肤因长期摩擦而变硬的部位，callous 本义是"像老茧一样硬的"，引申为"冷酷无情的、麻木不仁的"。这里形容她对他人困境无动于衷的态度。