1. a person who treats serious matters lightly or frivolously
2. a person who wastes time on unimportant things

Examples

• Don’t be such a trifler when it comes to your studies.
• The committee dismissed him as a mere trifler who couldn’t be trusted with important decisions.
• She accused her brother of being a trifler who spent hours on video games instead of homework.
• The professor had no patience for triflers who didn’t take the research seriously.
• He was known as a trifler who jumped from hobby to hobby without mastering any.
• The boss fired the trifler who spent work hours browsing social media.