70 entries under underground topic. ×
| undercover(secret, clandestine, undisclosed, top-secret) | |
| underhand(clandestine, undisclosed) | |
| underhanded(clandestine, undisclosed) | |
| unenlightened(clandestine, undisclosed) | |
| unfrequented(clandestine, undisclosed) | |
| unintelligible(clandestine, undisclosed) | |
| unknown(clandestine, undisclosed) | |
| unpublished(clandestine, undisclosed) | |
| unseen(clandestine, undisclosed) | |
| veiled(clandestine, undisclosed) |
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| APA | Smart Define. (2016). restricted thesaurus. Retrieved September 24, 2026, from https://smartdefine.org/restricted/thesaurus/synonyms |
| Chicago | Smart Define. 2016. "restricted thesaurus" https://smartdefine.org/restricted/thesaurus/synonyms (accessed September 24, 2026). |
| Harvard | Smart Define 2016, restricted thesaurus, Smart Define, viewed 24 September, 2026, <https://smartdefine.org/restricted/thesaurus/synonyms>. |
| MLA | Smart Define. "restricted thesaurus" 26 February 2016. Web. 24 September 2026. <https://smartdefine.org/restricted/thesaurus/synonyms> |