/ ˈɪntələʊpə(r); NAmE ˈɪntərloʊpər/ noun
a person who is present in a place or a situation where they do not belong
SYN intruder
••
WORD ORIGIN
late 16th cent. (denoting an unauthorized trader trespassing on the rights of a trade monopoly): from inter- amid + -loper as in archaic landloper vagabond (from Middle Dutch landlooper ).