the word 'trespasser' is built upon the verb 'trespass', which entered english from old french. the french term 'trespasser' was a compound of the latin preposition 'trans', meaning "across, beyond", and the noun 'passus', meaning "a step or pace". literally, it meant "to step across or beyond". this literal sense evolved in legal and moral contexts to signify overstepping a boundary, limit, or law. the agent suffix '-er' was then appended, a common germanic construction, to create a noun meaning "one who steps across or beyond (a limit)", concretely referring to someone who unlawfully enters property or metaphorically to one who commits a sin or offense.

Structure: trespass + er trespass: from old french 'trespasser', meaning "to pass across, cross, trespass", itself from latin 'trans' (across) + 'passus' (step, pace). er: from old english '-ere', a suffix forming agent nouns indicating "one who does or performs an action".