Footnote

Noun

 * 1) A short piece of text, often numbered, placed at the bottom of a printed page, that adds a comment, citation, reference etc, to a designated part of the main text
 * 2)  An event of lesser importance than some larger event to which it is related

Verb

 * 1) To add footnotes to a text; to annotate

Thesaurus
adversaria, aide-memoire, annotation, apparatus criticus, comment, commentary, commentation, docket, entry, exegesis, gloss, item, jotting, marginal note, marginalia, memo, memoir, memorandum, memorial, minutes, notation, note, note of explanation, register, registry, reminder, scholia, scholium, word of explanation