Considerable means large enough to be worth noticing or thinking about. When your teacher assigns a considerable amount of homework, she's giving you a substantial pile of problems that will take real time to complete. When a basketball team wins by a considerable margin, they won by enough points that the outcome was never really in doubt.

The word suggests size or importance that matters. A considerable distance is far enough to affect your plans: you might need to pack snacks or plan for traffic. A considerable improvement means real progress you can see and measure. If your friend makes a considerable effort to help you with a project, they're putting in serious time and energy, working with you for hours or doing careful research to contribute in a meaningful way.

Notice that considerable doesn't always mean huge or enormous. A considerable number of students might be 30 kids, not 300. What makes something considerable is that it's substantial enough to make a difference or deserve attention. When someone has considerable talent at piano, they're genuinely skilled. When repairs cost a considerable sum, the price is high enough to require careful thought about whether to proceed.