Source : Webster's Revised Unabridged Dictionary (1913)

Investigation \In*ves`ti*ga"tion\, n. [L. investigatio: cf. F.
   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 mathematician; the investigations of
   the judge, the moralist.

Source : WordNet®

investigation
     n 1: an inquiry into unfamiliar or questionable activities;
          "there was a congressional probe into the scandal" [syn:
           {probe}]
     2: the work of inquiring into something thoroughly and
        systematically [syn: {investigating}]