planetary UK /ˈplænɪtəri/US /ˈplænɪˌtɛəri/adjective 4noun 1forms 1 adjective4 •Of, or relating to planets, or the orbital motion of planets. •Of, or relating to the whole Earth; global. •Epicyclic. •Of, or relating to the Earth; terrestrial. noun1 •A planetary nebula. formsplanetaries