Frivolous describes something that isn't serious or important, especially when it should be. When someone makes frivolous comments during an important discussion, they're being silly or flippant instead of thoughtful. When a judge dismisses a frivolous lawsuit, they're throwing out a case that wastes the court's time because it has no real merit.

The word often carries a hint of criticism. A frivolous purchase is something you buy on a whim that you don't really need, like spending your savings on a giant stuffed animal instead of something useful. Frivolous spending means wasting money on things that don't matter.

Sometimes frivolous simply means lighthearted or playful, without the negative edge. A frivolous afternoon might involve games and laughter rather than serious work. But usually, the word suggests that someone is treating something too lightly. If your teacher says you're being frivolous about your homework, they mean you're not taking it seriously enough.

The opposite of frivolous would be serious, important, or substantial. When something truly matters, frivolous behavior feels out of place.