To overshadow means to make something seem less important or impressive by comparison. When a famous musician performs at your school talent show, their performance might overshadow the other acts, even if those students did well too. The word suggests that one thing is so big, bright, or attention-grabbing that it casts everything else into shadow.

You might hear someone say that one sibling's achievements overshadowed the other's, meaning the first child got so much attention that the second child's accomplishments went unnoticed. A spectacular finale can overshadow the rest of a play. A scandal might overshadow a politician's policy achievements.

When a tall building overshadows a park, it blocks the sunlight and casts a shadow over it. Similarly, when one thing overshadows another, it blocks attention and recognition that might otherwise shine on the less prominent thing.

Notice that being overshadowed doesn't mean you've failed or done badly. A perfectly good performance can be overshadowed by a great one. A solid achievement can be overshadowed by an extraordinary one. The thing being overshadowed might still have real value, but it gets less attention because something else dominates the moment.