Source : Webster's Revised Unabridged Dictionary (1913)

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

Source : WordNet®

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