Depending on the meaning:
* Terrestrial: If "celestial" refers to the heavens, "terrestrial" refers to the Earth.
* Earthly: Similar to "terrestrial," this emphasizes the connection to the planet Earth.
* Mundane: This implies something ordinary and commonplace, in contrast to the extraordinary nature of the celestial.
* Material: If "celestial" refers to spiritual or non-physical things, "material" refers to the physical world.
Other possibilities:
* Infernal: This refers to hell or the underworld, a contrasting concept to the celestial.
* Subterranean: This refers to being underground, in contrast to being in the sky.
It's important to consider the specific context to choose the most appropriate opposite.
