The most direct word for someone who behaves as though they know everything is “know-it-all.” Other choices describe different parts of the behavior, such as being dogmatic, overconfident, opinionated, smug, or arrogant. These words are not interchangeable, so choose the one that matches what the person actually does.
Pick the Word That Matches the Behavior
- Know-it-all
- Dogmatic
- Opinionated
- Arrogant
- Overconfident
- Smug
- Presumptuous
- Conceited
- Cocksure
- Pedantic
- Self-important
- Didactic
Know-it-all
The clearest informal noun for a person who acts as though they know everything, often in an irritating way. Example: He can come across as a know-it-all when he corrects everyone.
Dogmatic
Describes someone who presents beliefs or opinions as unquestionably correct and is unwilling to consider alternatives. Example: She became dogmatic whenever the discussion turned to policy.
Opinionated
Means having and expressing strong opinions, often too readily. It does not necessarily mean the person claims expert knowledge. Example: He is opinionated and rarely keeps his views to himself.
Arrogant
Suggests an exaggerated sense of superiority, which may include assuming one’s knowledge or judgment is better than everyone else’s. Example: Her arrogant tone made it difficult for others to contribute.
Overconfident
Fits someone who has more confidence in their knowledge or ability than the situation justifies. Example: He was overconfident about a subject he had only recently started studying.
Smug
Describes self-satisfied confidence, especially when someone seems pleased with being right. Example: She gave a smug smile when the result confirmed her prediction.
Presumptuous
Applies when someone assumes knowledge, authority, or entitlement that they may not actually have. Example: It was presumptuous of him to speak for the entire group.
Conceited
Describes someone with an excessively high opinion of themselves. The focus is broader than knowledge alone. Example: He sounded conceited when he dismissed everyone else’s ideas.
Cocksure
An informal and often disapproving adjective for someone who is excessively sure of themselves. Example: She was cocksure about the outcome despite having little information.
Pedantic
Describes excessive concern with minor details, rules, or displaying technical correctness. A pedantic person may seem like a know-it-all, but the meanings are not identical. Example: His pedantic corrections kept interrupting the conversation.
Self-important
Fits someone who behaves as though their own status, views, or knowledge deserve more weight than other people’s. Example: The self-important lecture was not well received.
Didactic
Can describe someone who speaks in an overly instructional or lecturing way. It is especially useful when the issue is tone rather than confidence. Example: Her didactic manner made an ordinary discussion feel like a classroom lesson.
Choose Descriptions Carefully
Most of these terms are critical. If you need neutral workplace wording, describe the behavior instead: “he tends to present his view as definitive,” “she is reluctant to consider alternative explanations,” or “he frequently corrects colleagues on minor points.”
“Know-it-all” is the closest match to the title. “Pedantic,” “opinionated,” and “arrogant” describe related behaviors, not exact synonyms.