As thick as thieves
Firm and as thick as thieves are semantically related. In some cases you can use "Firm" instead an adjective phrase "As thick as thieves".
Firm
Firm adjective - Not showing weakness or uncertainty.
As thick as thieves and firm are semantically related. Sometimes you can use "As thick as thieves" instead an adjective "Firm".
Cite this Source
Firm and As thick as thieves. (2016). Retrieved 2026, July 27, from https://thesaurus.plus/related/as_thick_as_thieves/firm
As thick as thieves & Firm. N.p., 2016. Web. 27 Jul. 2026. <https://thesaurus.plus/related/as_thick_as_thieves/firm>.
Firm or As thick as thieves. 2016. Accessed July 27, 2026. https://thesaurus.plus/related/as_thick_as_thieves/firm.