IPA: /ˈtrɛspəsər/
KK: /ˈtrɛspəsər/
A person who enters someone else's property without permission.
The security guard caught the trespasser trying to climb over the fence.
Trespasser → It is formed from "trespass" (from Old French *trespasser*, meaning to pass beyond) and "-er" (meaning a person who). A trespasser is a person who passes beyond the limits or boundaries, typically without permission.
Think of someone who 'passes beyond' boundaries ('trespass') — the '-er' indicates that this person is the one doing the action.