60 entries under secret topic. ×
| clandestine(adjective, unknown, hidden, sly) | |
| buried(verb, adjective, unknown, hidden) | |
| covert(adjective, unknown, hidden, concealed) | |
| surreptitious(adjective, unknown, hidden, concealed) | |
| undercover(adjective, unknown, hidden, spy) | |
| hidden(verb, adjective, unknown, concealed) | |
| concealed(adjective, unknown, hidden, spy) | |
| hole-and-corner(adjective, hidden, spy, covert) | |
| furtive(adjective, obscure, unknown, hidden) | |
| hush-hush(adjective, hidden, spy, clandestine) | |
| alternative(adjective, secretive, subversive, dissident) | |
| avant-garde(adjective, secretive, subversive, dissident) | |
| private(adjective, obscure, unknown, hidden) | |
| revolutionary(adjective, subversive) | |
| underhand(hidden, spy, clandestine, fraudulent) | |
| fifth column(noun, expression, subway, subversives) | |
| secluded(adjective, obscure, unknown, hidden) | |
| under wraps(expression, adjective, idiom, hidden) | |
| clouded(obscure, unknown, hidden, concealed) | |
| experimental(adjective, subversive) |
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| APA | Smart Define. (2015). underground thesaurus. Retrieved September 25, 2026, from https://smartdefine.org/underground/thesaurus/synonyms |
| Chicago | Smart Define. 2015. "underground thesaurus" https://smartdefine.org/underground/thesaurus/synonyms (accessed September 25, 2026). |
| Harvard | Smart Define 2015, underground thesaurus, Smart Define, viewed 25 September, 2026, <https://smartdefine.org/underground/thesaurus/synonyms>. |
| MLA | Smart Define. "underground thesaurus" 3 November 2015. Web. 25 September 2026. <https://smartdefine.org/underground/thesaurus/synonyms> |