n. 1. One who intrudes; one who thrusts himself in, or enters without right, or without leave or welcome; a trespasser. [ 1913 Webster ]
They were all strangers and intruders. Locke. [ 1913 Webster ]
2.Specifically: A person who enters a private residence or place of business with the intention to perform a criminal act; as, killed by an intruder. [ PJC ]