Essential
Essential adjective - Impossible to do without.
Usage example: a well-stocked public library is essential for the well-being of a community
Key is a synonym for essential in fundamental topic. In some cases you can use "Key" instead the word "Essential" as an adjective or a noun, when it comes to topics like basic, property, vital, crucial.
Key
Key adjective - Of the greatest possible importance.
Usage example: first—and this is key—I wasn't even there that evening
Essential is a synonym for key in fundamental topic. You can use "Essential" instead the word "Key" as an adjective or a noun, if it concerns topics such as property, condition, crucial, basic.
Mutual synonyms
Related pairs
How words are described
Both words in one sentence
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There are only two flippers, one ramp, and a half-dozen key targets (the genie and five "Golden Symbols") that are essential for the player to focus on.
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The characters know that an amber key and preventing a disaster are essential to getting home.
Source: Red Herring - The Power of Blood: It turns out that Celestia's blood was a key component in perfecting the ponification serum, while Discord's was essential in creating the cure.
Source: Fanfic / The Negotiations-verse
Cite this Source
Key and Essential. (2016). Retrieved 2026, August 14, from https://thesaurus.plus/related/essential/key
Essential & Key. N.p., 2016. Web. 14 Aug. 2026. <https://thesaurus.plus/related/essential/key>.
Key or Essential. 2016. Accessed August 14, 2026. https://thesaurus.plus/related/essential/key.
Google Ngram Viewer shows how "essential" and "key" have occurred on timeline