Source : Webster's Revised Unabridged Dictionary (1913)

Trespasser \Tres"pass*er\, n.
   One who commits a trespass; as:
   (a) (Law) One who enters upon another's land, or violates his
       rights.
   (b) A transgressor of the moral law; an offender; a sinner.

Source : WordNet®

trespasser
     n : someone who intrudes on the privacy or property of another
         without permission [syn: {intruder}, {interloper}]