63 entries under underground topic. ×

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on the QT(expression, idiom, obscure, unknown, clandestine)
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private(obscure, unknown, clandestine, undisclosed)
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restricted(adjective, clandestine, undisclosed, surreptitious)
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retired(obscure, deep, unknown, clandestine)
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secluded(obscure, unknown, clandestine, undisclosed)
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secretive(clandestine, undisclosed)
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sneak(clandestine, undisclosed)
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stealthy(clandestine, undisclosed)
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sub-rosa(clandestine, undisclosed)
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surreptitious(clandestine, undisclosed)
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top-secret(clandestine, undisclosed)
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top secret(expression, clandestine, undisclosed)
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unacknowledged(clandestine, undisclosed)
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under-the-table(clandestine, undisclosed)
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under false pretense(expression, idiom, clandestine, undisclosed)
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under wraps(expression, cover, obscure, dark, equivocal)
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undercover(clandestine, undisclosed)
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underhanded(adjective, false, misleading, clandestine)
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unenlightened(obscure, deep, unknown, clandestine)
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unfrequented(obscure, deep, unknown, clandestine)
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APASmart Define. (2016). ambiguous thesaurus. Retrieved September 23, 2026, from https://smartdefine.org/ambiguous/thesaurus/synonyms
ChicagoSmart Define. 2016. "ambiguous thesaurus" https://smartdefine.org/ambiguous/thesaurus/synonyms (accessed September 23, 2026).
HarvardSmart Define 2016, ambiguous thesaurus, Smart Define, viewed 23 September, 2026, <https://smartdefine.org/ambiguous/thesaurus/synonyms>.
MLASmart Define. "ambiguous thesaurus" 29 March 2016. Web. 23 September 2026. <https://smartdefine.org/ambiguous/thesaurus/synonyms>