12 Words for Someone Who Thinks They Know Everything

We’ve all met someone who thinks they know everything even though they don’t! But is there a single word or phrase that describes such a person?

In this article, we’ve provided just that – a whole list of words and phrases that you can use when you meet a person that thinks they’re an expert on everything! So, read on!

Words for Someone Who Thinks They Know Everything

  • Know-it-all
  • Arrogant
  • Wisenheimer
  • Self-righteous
  • Big-headed
  • Overconfident
  • Grandiose
  • Smart alek
  • Wiseacre
  • Smarty-pants
  • Swellhead
  • Wise guy


  • People frequently use the phrase “know-it-all” in informal settings to refer to someone who thinks they know everything.
  • When someone deems themselves superior for their knowledge, you might call them “arrogant.”
  • “Wisenheimer” is another informal word that expresses disapproval of a person’s know-it-all tendencies.

Before you go! We still need to discuss our three favorite terms that describe a person who thinks they know everything.

Moreover, we’ll provide some helpful examples so you can see these words in action!


If you’re looking for what to call a person who thinks they know everything, the most popular term people go for is “know-it-all.”

Merriam-Webster defines this phrase as “one who claims to know everything.” Therefore, this phrase is a perfect synonym!

However, the term “know-it-all” is informal. Therefore, you should avoid using it in formal settings such as work or school. It would not be suitable to use in professional correspondence. Moreover, it would not be appropriate for formal or academic writing either.

Nonetheless, you can use this phrase to express disapproval when a person thinks they know it all in casual or social circumstances.

Finally, let’s see a couple of example sentences making use of this phrase:

I like Ted, but he’s a bit of a know-it-all and it’s something a chore to talk to him.

Remember to let other people speak during the meeting – you don’t want to sound like a know-it-all.


“Arrogant” is another word to describe someone who thinks they know everything. This word is suitable since a person who thinks they know more than everyone else often thinks they are superior to others.

Merriam-Webster defines “arrogant” as “showing an offensive attitude of superiority.” Therefore, this is not a direct synonym, as a person can be arrogant for more reasons than simply thinking they are smarter than everyone else.

Nonetheless, if someone thinks they are superior because of their knowledge, they can certainly be described as “arrogant.”

The term “arrogant” is suitably formal to use in all kinds of circumstances. However, it can come across as rather confrontational. Therefore, we recommend using it with caution at work or otherwise!

Finally, let’s see this word employed in some example sentences:

Some would say that he behaves that way because he is confident, but I find him arrogant.

To think you know everything is not only arrogant, but it exhibits, quite embarrassingly, how little you truly know.


A further word for a person who thinks they know everything is a “wisenheimer.”

Google’s English Dictionary defines a “wisenheimer” as “a person who behaves in an irritatingly smug or arrogant fashion, typically by making clever remarks and displaying their knowledge.”

As you can see, “wisenheimer” is a good example of how to describe a person who thinks they know everything in a disapproving way.

Additionally, “wisenheimer” is considered somewhat informal and confrontational. Therefore, you should use it with caution in the workplace.

However, it is a funny word to use when complaining about someone’s behavior among your friends or family.

Lastly, let’s see this term used in a sentence or two:

She’s a complete wisenheimer, and it drives everyone around her crazy.

I’d rewrite paragraph 4 – it makes you look like a wisenheimer.