footnote
US /ˈfʊt.noʊt/
UK /ˈfʊt.noʊt/

1.
an additional piece of information printed at the bottom of a page
:
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The author included a footnote to explain the historical context.
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Please check the footnotes for more details.
2.
a minor or less important part of something
:
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His role in the project was merely a footnote.
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That incident became a mere footnote in history.
1.
to add a footnote to (a text or document)
:
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She decided to footnote the controversial statement.
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You should always footnote your sources in academic papers.