‘On a Side Note’: Definition, Meaning, and Examples

By Sophia Merton, updated on November 4, 2022

What does it mean when someone says ‘on a side note’? In this article, we’re going to explore the definition of this phrase and its origin and look at examples of the idiom in a sentence.b

‘On a side note’ is a phrase that is used before making a statement that is only partially related to a subject that is being discussed. It also has a more literal meaning that references a note that’s been made in the margins of a text, document, or book.

What Does ‘On a Side Note’ Mean?

The term ‘side note’ (also sometimes written as ‘sidenote’) has two primary definitions, which are:

  • ‘A note in the margins of a book, document, etc.’
  • ‘Something such as a fact or comment that is partially related to the main topic being discussed or written about’

When someone says ‘on a side note,’ they are most likely referring to the second definition listed above. Here’s an example:

  • We need to talk about what to make for dinner before I go to the store. On a side note, I cracked one of our plates this morning, so we need to order a replacement.

In some instances, it’s possible that the phrase ‘on a side note’ is being used in the more literal definition, referring to a note in the margins of a text. For example, someone might say:

  • You can see on a side note I’ve made in the text that there are different possible translations of this word.

When ‘on a side note’ is used in this way, the more proper preposition to use would be ‘in,’ as in ‘in a side note.’ That being said, you still might hear someone use the preposition 'on' when directing your attention to a physical side note in a text.

‘As a Side Note’ Vs. ‘On a Side Note’

You might also hear someone use the phrase ‘as a side note’ in a way that is basically interchangeable with ‘on a side note.’ You can use the Google Books nGram Viewer to see that the phrase ‘as a side note’ is slightly more common than ‘on a side note’ when searching through English books from the year 1800 to 2008.

Even though 'as a side note' appears to be more common than 'on a side note,' you can expect that anyone who understands what one of these phrases means will not be confused if you were to use the version using the alternative preposition to get your point across.

What’s the Origin of This Idiom?

It is difficult to determine the precise moment when people started using the phrase ‘on a side note’ as a way of connecting a partially related point to the topic being discussed.

Using the Google Books nGram Viewer linked above, though, we can see that the usage of the phrase in the books scoured by Google doesn’t begin until the late 1980s. ‘As a side note,’ however, appears as early as the 1860s and becomes more frequently used in the mid-1930s.

The Origin of ‘Side Note’

The term ‘side note’, meaning a ‘note made or placed at the side of a written or printed page,’ dates back to at least 1776.

The word ‘side’ is a late Old English word that is connected to the Old Norse word ‘siðr.’

‘Note,’ on the other hand, has its roots as a musical term as far back as 1300 and dates from the early 14th century with the meaning ‘notice, attention.’

It wasn’t until about the 1550s that the word 'note' started to be used in reference to ‘ a mark in the margin of a book calling attention to something in the text.’

Though there isn't a ton of available information about the origin of the phrase 'on a side note,' it is interesting to try and imagine how it emerged. In a text or document, a side note is something written in the margins that are related to a specific point made on the page. When using 'on a side note' in conversation or in writing, you are essentially referring to the main topic as the text in a figurative book and the comment you are about to make as a note in the margins.

How to Use ‘On a Side Note’ in a Sentence

Now that we’ve taken a look at what ‘on a side note’ means and its origin as a phrase let's look at how you can use this idiom in a sentence. Because of the meaning of the phrase, it is commonly used at the beginning of a sentence that follows a statement regarding the main topic being discussed.

  • I am leaving for work at 8 am on Friday. On a side note, I have a doctor’s appointment in the afternoon, so I’ll be late for dinner.
  • Losing that vendor was really the canary in a coal mine for the business. On a side note, I’m going to start sending out resumes next week.
  • This new software is becoming the bane of my existence. On a side note, I think it might be time to replace the batteries in our computer.
  • The price of gas is getting so outrageous that I’ve started biking to work when the weather is nice. On a side note, do you know how often the public buses run here?
  • We need to leave early tomorrow if we want to find parking for the event. On a side note, don’t forget to bring some extra water bottles. It’s going to be hot, and I don’t want us to get dehydrated.
  • I’ve always been fascinated by Norse mythology. On a side note, did you hear that they recently found a huge cache of Viking coins in Sweden?

These sentences can help you get a sense of how the phrase ‘on a side note’ can be used in everyday speech or writing. If you want to make a point that is loosely related to the main topic, but you want to make it clear that you are deviating from the primary subject, you can use this idiom for a better conversational flow.

Similar Phrases to ‘On a Side Note’

There are a number of other phrases that can be used in much the same way as ‘on a side note.’ Each of these has slightly different meanings, but they are all used to connect a slightly related point to the broader topic being discussed:

  • By the way
  • Additionally
  • Not to mention
  • Relatedly
  • More to the point
  • Parenthetically
  • Incidentally

‘On a Side Note’: Final Thoughts

‘On a side note’ and ‘as a side note’ are very useful phrases both in writing and speaking. If you want to make a point but feel it is necessary to make it clear that you are slightly deviating from the topic at hand, this is the perfect idiom to use.

By bridging the main topic and the side topic together with ‘on a side note,’ you are ensuring that your reader or listener understands that you are branching away from the primary topic for a moment. Without a phrase like this to help connect the partially related points, you might find that the people you are communicating with think that you are making a total non sequitur.

If you’re just beginning the journey to learning about English idioms and phrases, the whole thing can feel a bit overwhelming. Over time, you’ll find that you are enriching your vocabulary in a way that makes you a much more effective speaker, writer, and communicator.

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Written By:
Sophia Merton
Sophia Merton is one of the lead freelance writers for WritingTips.org. Sophia received her BA from Vassar College. She is passionate about reading, writing, and the written word. Her goal is to help everyone, whether native English speaker or not, learn how to write and speak with perfect English.

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