Even editors (especially editors, who need to know what they don’t know more than most people) need to look things up sometimes. It could be a spelling you can never remember or the way a word is hyphenated in x style guide. Sometimes you just come across a word you don’t know at all, and this happened to me while working on a literary article.
So, what is a deuteragonist in a plot or play?
We know what a protagonist is – the main, central character. And an antagonist is the one who is against them. But the deuteragonist is the second most important person in a narrative – second to the protagonist. This could be the antagonist, but is more likely to be a secondary character, a sidekick, a faithful friend.