65 entries under underground topic. ×

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dissimulated(clandestine, undisclosed)
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in ambush(expression, clandestine, undisclosed)
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inside(personal, clandestine, undisclosed, confidential)
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mystic(obscure, unknown, clandestine, undisclosed)
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mystical(obscure, unknown, clandestine, undisclosed)
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occult(obscure, unknown, clandestine, undisclosed)
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on the QT(expression, idiom, obscure, unknown, clandestine)
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restricted(clandestine, undisclosed)
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sly(clandestine, undisclosed)
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sneak(clandestine, undisclosed)
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sneaky(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, clandestine, undisclosed)
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APASmart Define. (2015). retired thesaurus. Retrieved September 28, 2026, from https://smartdefine.org/retired/thesaurus/synonyms
ChicagoSmart Define. 2015. "retired thesaurus" https://smartdefine.org/retired/thesaurus/synonyms (accessed September 28, 2026).
HarvardSmart Define 2015, retired thesaurus, Smart Define, viewed 28 September, 2026, <https://smartdefine.org/retired/thesaurus/synonyms>.
MLASmart Define. "retired thesaurus" 10 April 2015. Web. 28 September 2026. <https://smartdefine.org/retired/thesaurus/synonyms>