private detective
noun [ C ] uk/ˌpraɪ.vət dɪˈtek.tɪv/ us/ˌpraɪ.vət dɪˈtek.tɪv/ (also private investigator); (informal private eye)
私人侦探
a person whose job is discovering information about people. A private detective is not a government employee or a police officer
She hired a private detective to find out if her husband was having an affair. 她雇了一名私人侦探，调查她丈夫是不是有外遇。