Sidenote

Part of speech: noun

Definitions

1. A short note written in the margin of a page ; a brief incidental remark or aside made in passing ; a note printed alongside the main body of text
2. A marginal annotation added beside writing on a page ; an informal comment or digression offered in passing ; a small explanatory note set at the side of the main text
3. A brief note jotted in the margin ; a passing remark or aside that is not part of the main discussion ; a commentary printed beside the principal text on a page

Etymology: "Sidenote" is a plain compound of "side" and "note." "Side" comes from Old English "sīde," meaning the flank or edge of a body, which over time came to mean the edge or margin of anything, such as a page. "Note" comes from Latin "nota," a mark or sign, which in English came to mean a brief written record. Put together, a sidenote is a note written in the side margin of a text, which is exactly what the word still describes: a short comment set apart from the main body of writing.

Synonyms: footnote, annotation, aside, marginalia