His conscientious approach to his duties made him an invaluable employee.

conscientious 是由名词 conscience（良心）加上形容词后缀 -ious 构成的形容词。conscience 来自拉丁语，表示"道德意识、良知"。后缀 -ious 表示"具有...特性的"。 conscientious 形容一个人做事认真负责、一丝不苟，因为遵循内心的道德准则。