Interstellar is an adjective that refers to the space between stars or relating to the stars. Some synonyms for interstellar include extragalactic, intergalactic, interplanetary, and cosmic. Extragalactic pertains to or originating from beyond the Milky Way galaxy while intergalactic relates to the space between galaxies. Interplanetary describes the space between planets in our solar system. Cosmic is a broad term that encompasses the universe. Other synonyms for interstellar include astral, stellar, celestial, and galactic. Astral refers to the stars and planets, while stellar refers to stars specifically. Celestial describes anything related to the sky, while galactic refers to our galaxy, the Milky Way.