Subterrestrial is a word that describes something that is underground or beneath the surface. There are various synonyms for the word subterrestrial, including subterranean, subterraneous, underground, below ground, under the earth, earthbound, and earthy. These words can be used interchangeably to describe things such as caves, tunnels, mines, or even creatures that live beneath the surface. The word subterrestrial can also be used metaphorically to describe things that are hidden or concealed, such as secrets, motives, or agendas that are not immediately apparent. The synonyms for subterrestrial provide a range of options for writers and speakers to use when describing things that are below the surface.