Noun

• S: (n) prowler, sneak, stalker (someone who prowls or sneaks about; usually with unlawful intentions)
• direct hypernym / inherited hypernym / sister term
• S: (n) intruder, interloper, trespasser (someone who intrudes on the privacy or property of another without permission)
• S: (n) boarder (someone who forces their way aboard ship) "stand by to repel boarders"
• S: (n) gatecrasher, crasher, unwelcome guest (someone who gets in (to a party) without an invitation or without paying)
• S: (n) infiltrator (an intruder (as troops) with hostile intent)
• S: (n) invader, encroacher (someone who enters by force in order to conquer)
• S: (n) penetrator (an intruder who passes into or through (often by overcoming resistance))
• S: (n) prowler, sneak, stalker (someone who prowls or sneaks about; usually with unlawful intentions)
• S: (n) pusher, thruster (one who intrudes or pushes himself forward)
• S: (n) squatter (someone who settles on land without right or title)
• S: (n) stranger, alien, unknown (anyone who does not belong in the environment in which they are found)
• derivationally related form