also sidenote, "note made or placed at the side of a written or printed page," 1776, from side (adj.) + note (n.). A marginal note, as distinguished from a footnote.
Entries linking to side-note
side adj.
late Old English, "long, broad, spacious; extending lengthwise," from side (n.). Compare Old Norse siðr "long, hanging down." From late 14c. as "being from or toward the side," hence also "subordinate." Also "apart from the main course" of anything, as in side-road (1854); side-trip (1911). In side-eye (by 1922) the notion is "directed sideways."
note n.
c. 1300, "a song, music, melody; instrumental music; a bird-song; a musical note of a definite pitch," from Old French note and directly from Latin nota "letter, character, note," originally "a mark, sign, means of recognition," which traditionally has been connected to notus, past participle of noscere "to come to know," but de Vaan reports this is "impossible," and with no attractive alternative explanation, it is of unknown origin.
Meaning "notice, attention" is from early 14c.; that of "reputation, fame" is from late 14c. From late 14c. as "mark, sign, or token by which a thing may be known." From late 14c. as "a sign by which a musical tone is represented to the eye." Meaning "a brief written abstract of facts" is from 1540s; meaning "a short, informal written communication" is from 1590s. From 1550s as "a mark in the margin of a book calling attention to something in the text," hence "a statement subsidiary to the text adding or elucidating something." From 1680s as "a paper acknowledging a debts, etc." In perfumery, "a basic component of a fragrance which gives it its character," by 1905.
footnote n.
also foot-note, in printing, "a note at the bottom of a page as an appendage to some part of the text," 1841, from foot (n.) "lower end of a document" (1660s) + note (n.). So called from its original position at the foot of a page. Also sometimes formerly bottom note. As a verb, from 1864. Related: Footnoted; footnoting.