59 entries under underground topic. ×

11
recondite(adjective, evil, obscure, difficult, strange)
10
arcane(adjective, evil, obscure, solid, strange)
10
mystical(adjective, hard, evil, obscure, strange)
8
hush-hush(adjective, quiet, separate, reserved, secret)
8
undercover(adjective, secret, spy, clandestine)
7
deep(adjective, hard, evil, obscure, complex)
6
close(adjective, quiet, solid, humble, shy)
4
restricted(clandestine, undisclosed)
4
secretive(adjective, quiet, obscure, plain, strange)
3
discreet(personal, imperceptible, unremarkable, unobtrusive)
3
out-of-the-way(adjective, close, quiet, separate, shy)
3
sneaky(adjective, secret, private, clandestine)
3
unintelligible(adjective, hard, obscure, solid, dark)
3
unpublished(adjective, clandestine, undisclosed)
2
ambiguous(adjective, cover, obscure, dark, doubtful)
2
backstairs(unknowing, clandestine, undisclosed, hermetical)
2
classified(personal, clandestine, undisclosed, confidential)
2
cloak-and-dagger(clandestine, fraudulent, undisclosed)
2
reticent(adjective, quiet, obscure, humble, distant)
2
retired(adjective, close, quiet, separate, humble)
11 years ago|29k views|share |citing 
APASmart Define. (2015). hidden thesaurus. Retrieved September 23, 2026, from https://smartdefine.org/hidden/thesaurus/synonyms
ChicagoSmart Define. 2015. "hidden thesaurus" https://smartdefine.org/hidden/thesaurus/synonyms (accessed September 23, 2026).
HarvardSmart Define 2015, hidden thesaurus, Smart Define, viewed 23 September, 2026, <https://smartdefine.org/hidden/thesaurus/synonyms>.
MLASmart Define. "hidden thesaurus" 10 April 2015. Web. 23 September 2026. <https://smartdefine.org/hidden/thesaurus/synonyms>