in ‧ ter ‧ lop ‧ er /ˈɪntələʊpə $ -tərloʊpər/ BrE AmE noun [countable]
[ Date: 1500-1600 ; Origin: inter- + -loper (perhaps from Old English hleapan 'to jump' or Middle Dutch lopen 'to run' ) ]
someone who enters a place or group where they should not be