68 entries under adjective topic. ×

14
surreptitious(dishonest, secret, hidden, spy)
13
clandestine(adverb, show, dishonest, secret)
13
secret(quiet, show, dishonest, hidden)
12
covert(show, secret, reticent, hidden)
11
hush-hush(adverb, show, informal, dishonest)
11
underground(secret, unknown, hidden, spy)
9
furtive(dishonest, secret, reticent, hidden)
8
hidden(secret, spy, clandestine, underground)
8
hole-and-corner(secret, private, hidden, spy)
8
hugger-mugger(quiet, intriguing)
7
confidential(secret, hidden, spy, clandestine)
7
private(secret, unknown, hidden, spy)
7
stealthy(quiet, dishonest, secret, hidden)
7
underhand(deceitful, secret, hidden, spy)
6
concealed(obscure, dishonest, secret, hidden)
6
under wraps(expression, idiom, show, dishonest)
6
secluded(secret, unknown, hidden, underground)
5
cloak-and-dagger(show, full, secret, sly)
5
spy(secret, warning, hidden, covert)
4
backstairs(mysterious, private, reticent, taciturn)
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APASmart Define. (2015). undercover thesaurus. Retrieved September 24, 2026, from https://smartdefine.org/undercover/thesaurus/synonyms
ChicagoSmart Define. 2015. "undercover thesaurus" https://smartdefine.org/undercover/thesaurus/synonyms (accessed September 24, 2026).
HarvardSmart Define 2015, undercover thesaurus, Smart Define, viewed 24 September, 2026, <https://smartdefine.org/undercover/thesaurus/synonyms>.
MLASmart Define. "undercover thesaurus" 13 April 2015. Web. 24 September 2026. <https://smartdefine.org/undercover/thesaurus/synonyms>