1. excessively or unnecessarily serious in manner, tone, or attitude
Usage: informal; often used to describe someone who takes things too seriously or lacks humor

Examples

• He has an overserious attitude about everything, even when joking around.
• Don't be so overserious—it was just a harmless prank.
• Her overserious demeanor made it hard for her to connect with the other kids at the party.
• The movie's overserious tone made what should have been a fun adventure feel tedious.
• He tends to be overserious about minor mistakes at work.
• She appreciated his humor because he wasn't overserious like most of her colleagues.