# intruder

/ˌɪnˈtɹudɝ/ (US) · /ɪntɹˈuːdɐ/ (UK) · CEFR B2 · Noun

Source: https://englishreference.com/word/intruder
Updated: 2026-05-06

## Definition

a person who enters a place without permission, often to steal something or cause trouble.

For teachers: a person who enters a building, grounds, or private property without invitation or legal right.

## Examples

- The security alarm went off when the intruder broke a window.
- The homeowner called the police after seeing an unknown intruder on the backyard security camera.
- While the motion sensors are designed to detect a human intruder, they are frequently triggered by local wildlife or swaying tree branches.

## Usage notes

- Often used in legal or security contexts to distinguish between a guest and an unauthorised person.

---

From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.