32
underground(adjective, surface, depth)
17
below
16
beneath
14
subterraneous(adjective, depth)
13
buried(adjective, hidden, underground, covered, depth)
12
subterrestrial(adjective, surface, hidden, underground, covered)
11
ulterior
8
deep(adjective, low, down, far, depth)
6
secret(adjective, hidden, underground)
5
submarine(noun, depth)
5
cave
5
cavern
5
clandestine
5
furtive
5
subaqueous(adjective, depth)
5
sunken(adjective, hidden, underground, covered)
4
covert(adjective, hidden, underground)
4
covered(adjective, hidden, underground)
4
underfoot(adjective, hidden, underground, covered)
3
hidden
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APASmart Define. (2015). subterranean thesaurus. Retrieved September 20, 2026, from https://smartdefine.org/subterranean/thesaurus/synonyms
ChicagoSmart Define. 2015. "subterranean thesaurus" https://smartdefine.org/subterranean/thesaurus/synonyms (accessed September 20, 2026).
HarvardSmart Define 2015, subterranean thesaurus, Smart Define, viewed 20 September, 2026, <https://smartdefine.org/subterranean/thesaurus/synonyms>.
MLASmart Define. "subterranean thesaurus" 13 April 2015. Web. 20 September 2026. <https://smartdefine.org/subterranean/thesaurus/synonyms>