Open
Open adjective - Free in expressing one's true feelings and opinions.
Usage example: a talkative and open child who tells people more than they want to know
Plain is a synonym for open in clear topic. In some cases you can use "Plain" instead an adjective "Open", when it comes to topics like speech, honest, obvious, overt.
Plain
Plain adjective - Free in expressing one's true feelings and opinions.
Usage example: their piano teacher is honest and plain, if not always tactful
Open is a synonym for plain in clear topic. You can use "Open" instead an adjective "Plain", if it concerns topics such as speech, candid, evident, straightforward.
Mutual synonyms
Both words in one sentence
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Their identities and jobs seem to be, at best, open secrets (if not just plain "open.")
Source: Overt Operative -
Kunzite in particular stands out among the four, as he is the only one with an open collar, cape, drop earrings instead of plain studs, and shoes as opposed to tall boots.
Source: Anime / Sailor Moon Crystal -
While in the movie he is still portrayed as a Noble Demon in comparison to Tavington's plain demon, he still holds the colonists in open contempt and disdain.
Source: Film / The Patriot
Cite this Source
Plain and Open. (2016). Retrieved 2026, August 14, from https://thesaurus.plus/related/open/plain
Open & Plain. N.p., 2016. Web. 14 Aug. 2026. <https://thesaurus.plus/related/open/plain>.
Plain or Open. 2016. Accessed August 14, 2026. https://thesaurus.plus/related/open/plain.
Google Ngram Viewer shows how "open" and "plain" have occurred on timeline