intruder
UK: ɪnˈtruːdə | US: ɪnˈtruːdər
n. a person who enters a place or situation without permission or invitation
n. someone who interferes in the affairs of others
The word "intruder" originates from Latin intrudere ("to thrust into"), combining in- (into) and trudere (to push). The root trud evolved into Old French intruder, later adopted into Middle English. The suffix -er denotes an agent, forming a noun meaning "one who pushes into." This reflects the literal and figurative sense of forcing oneself into a space or situation uninvited.
The security system alerted us to an intruder in the building.
She felt like an intruder at the private family gathering.
Wildlife cameras captured an intruder entering the restricted area.
The dog barked fiercely at the perceived intruder.
Hackers are often seen as digital intruders in secure networks.