Subtext

wiktionary

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sub- +‎  text

etymonline

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subtext (n.)

"underlying theme of a work of literature," 1950, from sub- + text (n.). Originally a term in Konstantin Stanislavsky's theory of acting. Earlier it was used in a literal sense of "text appearing below other text on a page" (1726). Latin subtextere meant "to weave under, work in below."