Here are some synonyms for "cosmic," depending on the specific context:

General:

* Universal

* Celestial

* Astral

* Starry

* Galactic

* Extraterrestrial

* Interplanetary

* Cosmological

* Infinite

* Vast

* Grand

* Immense

More specific:

* Heavenly (referring to the heavens)

* Stellar (referring to stars)

* Cosmogonic (referring to the origin of the universe)

* Extraneous (referring to something outside the earth)

* Transcendent (referring to something beyond the ordinary)

The best synonym for "cosmic" will depend on the specific context in which you are using it.