trespasser
    n 1: someone who intrudes on the privacy or property of another
         without permission [syn: intruder, interloper,
         trespasser]

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.
       [1913 Webster]

TRESPASSER. One who commits a trespass. 
     2. A man is a trespasser by his own direct action he acts without any 
excuse; or he may be a trespasser in the execution of a legal process in an 
illegal manner; 1 Chit. Pl. 183: 2 John. Cas. 27; or when the court has no 
jurisdiction over the subject-matter when the court has jurisdiction but the 
proceeding is defective and void; when the process has been misapplied, as, 
when the defendant has taken A's goods on an execution against B; when the 
process has been abused 1 Chit. Pl. 183-187 in all these cases a man is a 
trespasser ab initio. And a person capable of giving his assent may become a 
trespasser, by an act subsequent to the tort. If, for example, a an take 
possession of land for the use of another, the latter may afterwards 
recognize and adopt the act; by so doing, he places himself in the situation 
of one who had previously commanded it, and consequently is himself a 
trespasser, if the other had no right to enter, nor he to command the entry. 
4 Inst. 317; Ham. N. P. 215. Vide 1 Rawle's R. 121.