| alternative(adjective, secret, secretive, subversive, dissident) | |
| avant-garde(adjective, secret, secretive, subversive, dissident) | |
| covertly(adverb, undercover) | |
| private(adjective, obscure, secret, unknown, hidden) | |
| revolutionary(adjective, secret, subversive) | |
| subterraneous(adjective, depth) | |
| underhand(secret, hidden, spy, clandestine, fraudulent) | |
| backstairs(clandestine, undisclosed) | |
| deep(adjective, obscure, down, unknown, far) | |
| fifth column(noun, expression, secret, subway, subversives) | |
| privately(adverb, undercover) | |
| secluded(adjective, obscure, secret, unknown, hidden) | |
| under wraps(expression, adjective, idiom, secret, hidden) | |
| Maquis | |
| belowground | |
| clouded(obscure, secret, unknown, hidden, concealed) | |
| experimental(adjective, secret, subversive) | |
| guerrilla | |
| in a cloud(expression, idiom, concealment) | |
| in a fog(expression, idiom, concealment) |
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| APA | Smart Define. (2015). underground thesaurus. Retrieved September 21, 2026, from https://smartdefine.org/underground/thesaurus/synonyms |
| Chicago | Smart Define. 2015. "underground thesaurus" https://smartdefine.org/underground/thesaurus/synonyms (accessed September 21, 2026). |
| Harvard | Smart Define 2015, underground thesaurus, Smart Define, viewed 21 September, 2026, <https://smartdefine.org/underground/thesaurus/synonyms>. |
| MLA | Smart Define. "underground thesaurus" 3 November 2015. Web. 21 September 2026. <https://smartdefine.org/underground/thesaurus/synonyms> |