Certain
Certain adjective - Having been established and usually not subject to change.
Usage example: a certain percentage of the profits will go to charity
Fluid
Fluid adjective - Likely to change frequently, suddenly, or unexpectedly.
Usage example: his arrival plans are fluid, so expect him anytime
Nearby Word: fluidity
Both words in one sentence
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When he was a toddler, Francis attempted to douse his teddy bear with lighter fluid and set it on fire (similar to certain people who kidnap other people) before Lois intervened.
Source: Troubling Unchildlike Behavior -
Later, Bob crashes his car and states that he was certain he changed the brake fluid.
Source: Western Animation / The Oblongs -
Shapeshifting Excludes Clothing: After a certain event, the only thing left of people are their clothes and pools of orange fluid.
Source: Anime / Neon Genesis Evangelion
Cite this Source
Fluid and Certain. (2016). Retrieved 2026, July 21, from https://thesaurus.plus/related/certain/fluid
Certain & Fluid. N.p., 2016. Web. 21 Jul. 2026. <https://thesaurus.plus/related/certain/fluid>.
Fluid or Certain. 2016. Accessed July 21, 2026. https://thesaurus.plus/related/certain/fluid.
Google Ngram Viewer shows how "certain" and "fluid" have occurred on timeline