alien [aliens](person, etc. from outside) noun [UK: ˈeɪ.liən] [US: ˈeɪ.liən]
stranger [strangers](person whom one does not know) noun [UK: ˈstreɪn.dʒə(r)] [US: ˈstreɪn.dʒər]He's quite formal when he meets a stranger. = Es muy ceremonioso cuando le presentan una persona desconocida.