60 entries under underground topic. ×

4
clandestine(adjective, special, intimate, personal)
4
restricted(adjective, secret, private, clandestine)
4
unrevealed(adjective, individual, essential, private, mental)
2
deep(noun, adjective, keen, sharp, smart)
1
backdoor(close, intimate, secret, private, clandestine)
1
backstairs(close, restricted, clandestine, discreet)
1
camouflaged(close, clandestine, undisclosed, furtive)
1
close(intimate, private, clandestine, central)
1
covert(clandestine, undisclosed)
1
cryptic(adjective, close, clandestine, undisclosed)
1
disguised(clandestine, undisclosed)
1
dissembled(close, restricted, clandestine, discreet)
1
dissimulated(close, restricted, clandestine, discreet)
1
furtive(close, clandestine, undisclosed)
1
in ambush(expression, close, restricted, clandestine)
1
incognito(close, restricted, clandestine, discreet)
1
mysterious(clandestine, undisclosed)
1
secretive(restricted, clandestine, discreet, undisclosed)
1
sly(sharp, smart, intelligent, clever, astute)
1
sneak(close, restricted, clandestine, discreet)
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APASmart Define. (2015). inside thesaurus. Retrieved September 22, 2026, from https://smartdefine.org/inside/thesaurus/synonyms
ChicagoSmart Define. 2015. "inside thesaurus" https://smartdefine.org/inside/thesaurus/synonyms (accessed September 22, 2026).
HarvardSmart Define 2015, inside thesaurus, Smart Define, viewed 22 September, 2026, <https://smartdefine.org/inside/thesaurus/synonyms>.
MLASmart Define. "inside thesaurus" 10 April 2015. Web. 22 September 2026. <https://smartdefine.org/inside/thesaurus/synonyms>