Sidenote, also known as a marginal note, is a reference or remark that is adjacent to the main text. However, there are several other words that can be used as synonyms for this term. One possible alternative is "digression," which implies a deviation from the main topic. Another is "footnote," which denotes a note placed at the bottom of the page. Other synonyms for sidenote include "annotation," "comment," "interpolation," "parenthesis," and "addendum," which all refer to supplementary information that is relevant to the topic at hand. Regardless of the term used, a sidenote can be an effective tool for providing additional context or clarification to a text.