Everyone was disappointed by his cowardice at the critical moment.

cowardice 是名词，由形容词 coward（懦弱的）加上名词后缀 -ice 构成，表示"懦弱、胆怯"这种品质或行为。后缀 -ice 常用于将形容词转化为抽象名词，表示某种性质或状态。