53 entries under underground topic. ×

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out-of-the-way(clandestine, undisclosed)
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restricted(adjective, secret, clandestine, undisclosed)
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retired(clandestine, undisclosed)
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strange(clandestine, undisclosed)
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subterrestrial
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top-secret(secret, clandestine, undisclosed)
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top secret(expression, clandestine, undisclosed)
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unacknowledged(clandestine, undisclosed)
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under false pretense(expression, idiom, clandestine, undisclosed)
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unenlightened(clandestine, undisclosed)
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unfrequented(clandestine, undisclosed)
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unintelligible(clandestine, undisclosed)
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unpublished(clandestine, undisclosed)
<123>
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APASmart Define. (2015). undercover thesaurus. Retrieved September 26, 2026, from https://smartdefine.org/undercover/thesaurus/synonyms
ChicagoSmart Define. 2015. "undercover thesaurus" https://smartdefine.org/undercover/thesaurus/synonyms (accessed September 26, 2026).
HarvardSmart Define 2015, undercover thesaurus, Smart Define, viewed 26 September, 2026, <https://smartdefine.org/undercover/thesaurus/synonyms>.
MLASmart Define. "undercover thesaurus" 13 April 2015. Web. 26 September 2026. <https://smartdefine.org/undercover/thesaurus/synonyms>