59 entries under underground topic. ×

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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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strange(obscure, unknown, clandestine, undisclosed)
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sub-rosa(clandestine, undisclosed)
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subterrestrial(adjective, hidden)
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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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underfoot(adjective, hidden)
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underhand(clandestine, undisclosed)
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underhanded(clandestine, undisclosed)
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unenlightened(obscure, unknown, clandestine, undisclosed)
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unfrequented(obscure, unknown, clandestine, undisclosed)
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unintelligible(obscure, unknown, clandestine, undisclosed)
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unpublished(obscure, unknown, clandestine, undisclosed)
<123>
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APASmart Define. (2015). covered thesaurus. Retrieved September 25, 2026, from https://smartdefine.org/covered/thesaurus/synonyms
ChicagoSmart Define. 2015. "covered thesaurus" https://smartdefine.org/covered/thesaurus/synonyms (accessed September 25, 2026).
HarvardSmart Define 2015, covered thesaurus, Smart Define, viewed 25 September, 2026, <https://smartdefine.org/covered/thesaurus/synonyms>.
MLASmart Define. "covered thesaurus" 13 April 2015. Web. 25 September 2026. <https://smartdefine.org/covered/thesaurus/synonyms>