To enter someone's property without permission; to intrude or encroach upon another's rights or domain.
From Old French 'trespasser' meaning 'to pass across', composed of 'tres-' (across) and 'passer' (to pass). Originally meant any kind of wrongdoing or sin, but gradually narrowed to specifically mean unlawful entry onto another's property.
The Lord's Prayer includes 'forgive us our trespasses' because 'trespass' originally meant any sin or wrongdoing, not just entering property illegally! The modern legal meaning is actually much narrower than the original religious sense of crossing moral boundaries.
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