Significantly means in a way that matters, makes a real difference, or is large enough to be important and noticeable.

When something changes significantly, the change is substantial and clearly observable. If your grades improve significantly, they might jump from a C to an A. If a runner significantly improves their mile time, they might drop from nine minutes to seven minutes.

Scientists use this word carefully. When they say two things are significantly different, they mean the difference is real and meaningful, not just due to random chance. If a new teaching method significantly improves reading scores, it means students actually learned noticeably more, not just one or two points better.

The word suggests that whatever happened is important enough to pay attention to. A significant amount of snow means enough to cancel school, not just a dusting. Contributing significantly to a group project means doing real work that matters, not just showing up. When your parents say your behavior has improved significantly, they mean they've noticed a genuine, meaningful change in how you act.