Definition
One who enters upon the land or property of another without right, license, or authority. In the most specific historical legal usage, an intruder is a stranger who enters upon land after the death of an ancestor, unlawfully, before the heir can take possession. More broadly, the term describes any person who enters or remains on property to which they have no legal claim or permission.
Common Language
Modern common usage (Wiktionary): Someone who intrudes.
Historical common usage (Webster's 1913): One who intrudes; one who thrusts himself in, or enters without right, or without leave or welcome; a trespasser.
The ordinary English meaning of intruder and the general legal meaning are close enough that the word rarely misleads a modern reader in isolation. The gap, however, is historical and technical: in classical common law, intruder was a term of art with a specific meaning tied to the moment of an ancestor's death and the heir's right of entry, distinguishing the intruder from a trespasser, abator, or disseisor in ways that determined available remedies. Webster's 1913 conflates intruder with trespasser, erasing this distinction — which is itself evidence that the technical meaning was already fading from general awareness by the turn of the twentieth century.
Common Confusion
INTRUDER vs. TRESPASSER: These terms are frequently used interchangeably in modern legal and common usage, but at common law they were distinct. A trespasser entered land in the possessor's lifetime without permission; an intruder in the technical sense entered specifically in the window between an ancestor's death and the heir's entry. The abator occupies a related but distinct position (entering between the death and the heir's entry to claim the freehold adversely). The distinctions matter primarily in historical property research; in modern criminal and tort law, the practical difference between intruder and trespasser is minimal and often jurisdiction-specific.
Why It Matters in Research
The historical technical meaning of intruder — tied specifically to inheritance and the race to possession after an ancestor's death — is largely obsolete in modern legal usage. Researchers working with older common law materials, particularly in property and real actions, will encounter intruder in this narrow sense and must resist reading it as a simple synonym for trespasser. The distinction mattered at common law because different remedies applied depending on whether the entrant was a trespasser, disseisor, abator, or intruder. The heir's remedy against an intruder in the historical sense was entry or a real action, not necessarily trespass.
In modern sources, intruder functions primarily in criminal law contexts — burglary, breaking and entering, home invasion, and self-defense statutes — where it broadly means any unauthorized entrant, with no inheritance dimension whatsoever. Researchers crossing between historical property materials and modern criminal or tort law must track which register they are working in.
The term also appears with increasing frequency in self-defense and castle doctrine cases, where courts must define who qualifies as an intruder for purposes of presumed-threat statutes. Here the legal meaning has expanded well beyond the historical property sense: an intruder may include someone who entered lawfully but refuses to leave, or someone who enters a curtilage rather than the dwelling itself. Jurisdictional variation in these statutes makes the term's scope in any given state dependent on the specific statutory language.
Historical Dictionary Support
Black's and Bouvier's are in close agreement, both defining intruder specifically as a stranger who enters land after an ancestor's death before the heir can enter. This is the classic common law technical definition, rooted in the law of real actions and the hierarchy of possessory rights at death. Anderson's is notably broader — "a person who enters upon land when he has no right" — which captures both the inheritance-specific meaning and the more general sense. Anderson's broader phrasing reflects a flattening of the technical term that was already underway by the late nineteenth century as real actions fell out of use.
What the historical dictionaries collectively miss is the term's migration into criminal law and self-defense doctrine, where it now does most of its modern legal work. None of the three sources address intruder in the context of burglary, home invasion, or the castle doctrine — concepts that now define how courts and legislatures actually use the word. Researchers relying solely on historical dictionary definitions will have an incomplete picture.
Jurisdictional Note
Modern self-defense and castle doctrine statutes vary significantly in how they define intruder, particularly whether the term extends to curtilage, vehicles, or places of business, and whether it includes persons who entered lawfully but whose license has been revoked. Researchers should not assume a uniform statutory meaning and should consult the specific jurisdiction's definitions.