Sleuth

from WordNet (r) 3.0 (2006)

sleuth
    n 1: a detective who follows a trail [syn: {sleuth},
         {sleuthhound}]
    v 1: watch, observe, or inquire secretly [syn: {spy}, {stag},
         {snoop}, {sleuth}]

from The Collaborative International Dictionary of English v.0.48

Sleuth \Sleuth\, n. [Icel. sl[=o][eth]. See {Slot} a track.]
   The track of man or beast as followed by the scent. [Scot.]
   --Halliwell.
   [1913 Webster]

from Moby Thesaurus II by Grady Ward, 1.0

33 Moby Thesaurus words for "sleuth":
      Bow Street runner, FBI, FBI agent, Federal, G-man, Secret Service,
      Sherlock, Sherlock Holmes, T-man, detective, dick, eye, fed,
      gumshoe, hawkshaw, hotel detective, house detective, house dick,
      inquiry agent, investigator, narc, operative, plainclothesman,
      police detective, private detective, private eye,
      private investigator, revenuer, shamus, snoop, store detective,
      tec, treasury agent