1) Analysis 2) Consultation 3) Counting 4) Enquiry 5) Examination 6) Inquiry 7) Investigating 8) Probe 9) Research 10) Review 11) Scrutiny 12) Shadowing 13) Surveillance 14) Trial 15) Wiretap 1) Enquiry 2) Examination 3) Exploration 4) French word used in English 5) Inquest 6) Inquiry 7) Inquisition 8) Inspection 9) Post-mortem 10) Probe 11) Reconnaissance 12) Research 13) Scouting 14) Study 15) Survey 
• (n.) The act of investigating; the process of inquiring into or following up; research; study; inquiry, esp. patient or thorough inquiry or examination; as, the investigations of the philosopher and the mathematician; the investigations of the judge, the moralist.
In·ves`ti·ga'tion noun [ Latin investigatio : confer French investigation .] The act of investigating; the process of inquiring into or following up; research; study; inquiry, esp. patient or thorough inquiry or examination; as, the investigations of the philosopher and the mathema...
[n] - the work of inquiring into something thoroughly and systematically
A quest to find the answer to a question using the scientific method
investigating noun the work of inquiring into something thoroughly and systematically
the act or process of investigating or the condition of being investigated. · a searching inquiry for ascertaining facts; detailed or careful examination.
an inquiry into unfamiliar or questionable activities