A side note is an additional piece of information that is not directly related to the main subject. If you are looking for synonyms for this term, you can go for phrases such as "incidentally," "by the way," or "additionally." A related term to this concept is "footnote," which is a written note at the bottom of a page that offers clarifying or explanatory information. Another synonym could be "annotation," which focuses on adding precise comments or explanations to a written text. Finally, other phrases that could be used as side note synonyms include "aside," "digression," or "tangent."".