66 entries under underground topic. ×

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ambiguous(obscure, unknown, clandestine, undisclosed)
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cloak-and-dagger(obscure, secret, unknown, clandestine)
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clouded(obscure, unknown, clandestine, undisclosed)
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conspiratorial(obscure, unknown, clandestine, undisclosed)
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covered(obscure, unknown, clandestine, undisclosed)
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deep(obscure, unknown, clandestine, undisclosed)
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enigmatical(obscure, unknown, clandestine, undisclosed)
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incognito(clandestine, undisclosed)
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mystic(obscure, unknown, clandestine, undisclosed)
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mystical(obscure, unknown, clandestine, undisclosed)
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obscure(unknown, clandestine, undisclosed, unrevealed)
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out-of-the-way(obscure, unknown, clandestine, undisclosed)
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recondite(obscure, unknown, clandestine, undisclosed)
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reticent(obscure, unknown, clandestine, undisclosed)
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retired(obscure, unknown, personal, clandestine)
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secluded(obscure, unknown, personal, clandestine)
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shrouded(obscure, unknown, clandestine, undisclosed)
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strange(obscure, unknown, clandestine, undisclosed)
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undercover(secret, clandestine, undisclosed, top-secret)
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underhand(clandestine, undisclosed)
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APASmart Define. (2015). classified thesaurus. Retrieved September 28, 2026, from https://smartdefine.org/classified/thesaurus/synonyms
ChicagoSmart Define. 2015. "classified thesaurus" https://smartdefine.org/classified/thesaurus/synonyms (accessed September 28, 2026).
HarvardSmart Define 2015, classified thesaurus, Smart Define, viewed 28 September, 2026, <https://smartdefine.org/classified/thesaurus/synonyms>.
MLASmart Define. "classified thesaurus" 14 April 2015. Web. 28 September 2026. <https://smartdefine.org/classified/thesaurus/synonyms>