A private investigator, also known as a PI, is a professional who investigates and gathers evidence on behalf of their clients. The term 'private investigator' can be broken down into five different words: DETECTIVE (9 letters), PEEPER (6 letters), GUMSHOE (7 letters), SPOTTER (7 letters), and OPERATIVE (9 letters). A DETECTIVE is a person who investigates crimes and collects evidence. A PEEPER is someone who secretly watches or observes people. A GUMSHOE is a slang term for a DETECTIVE, referring to the shoes they wear while investigating. A SPOTTER is someone who looks out for suspicious activity. Lastly, an OPERATIVE is a person who works undercover to gather information. All of these terms are used to describe a private investigator.