from The American Heritage® Dictionary of the English Language, 4th Edition
- n. See private investigator.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A private personal detective, employed to gather information about someone.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. someone who can be employed as a detective to collect information
From private investigator and its abbreviation P.I., through the homophonic term eye in place of "I", and the used of eye as a reference to survellience (Wiktionary)