57 entries under underground topic. ×

4
inside(adjective, special, intimate, secret, private)
4
stealthy(adjective, clandestine, undisclosed)
2
furtive(adjective, obscure, unknown, hidden, clandestine)
2
incognito(clandestine, undisclosed)
2
sneaky(adjective, sly, clandestine, fraudulent)
2
surreptitious(adjective, secret, clandestine, undisclosed)
2
undercover(adjective, secret, sly, clandestine)
1
arcane(adjective, obscure, intimate, private, unknown)
1
backstairs(adjective, clandestine, undisclosed)
1
cloak-and-dagger(obscure, secret, unknown, hidden, sly)
1
cryptic(adjective, obscure, unknown, clandestine)
1
esoteric(adjective, obscure, secret, unknown, clandestine)
1
obscure(adjective, unknown, clandestine, undisclosed)
1
recondite(adjective, obscure, unknown, clandestine)
1
secretive(adjective, clandestine, undisclosed)
1
sly(adjective, clandestine, fraudulent, undisclosed)
1
top secret(expression, idiom, clandestine, undisclosed)
1
under wraps(expression, secret, hidden, clandestine)
1
underhand(adjective, hidden, clandestine, fraudulent)
1
underhanded(adjective, clandestine, undisclosed)
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APASmart Define. (2015). closet thesaurus. Retrieved September 25, 2026, from https://smartdefine.org/closet/thesaurus/synonyms
ChicagoSmart Define. 2015. "closet thesaurus" https://smartdefine.org/closet/thesaurus/synonyms (accessed September 25, 2026).
HarvardSmart Define 2015, closet thesaurus, Smart Define, viewed 25 September, 2026, <https://smartdefine.org/closet/thesaurus/synonyms>.
MLASmart Define. "closet thesaurus" 30 September 2015. Web. 25 September 2026. <https://smartdefine.org/closet/thesaurus/synonyms>