Flat
Firm
Firm adjective - Having been established and usually not subject to change.
Usage example: the selling price of the house is firm, so there'll be no dickering
Flat is a synonym for firm in change topic. Sometimes you can use "Flat" instead an adjective "Firm", if it concerns topics such as unalterable.
How words are described
Cite this Source
Firm and Flat. (2016). Retrieved 2026, August 14, from https://thesaurus.plus/related/flat/firm
Flat & Firm. N.p., 2016. Web. 14 Aug. 2026. <https://thesaurus.plus/related/flat/firm>.
Firm or Flat. 2016. Accessed August 14, 2026. https://thesaurus.plus/related/flat/firm.
Google Ngram Viewer shows how "flat" and "firm" have occurred on timeline