Decided means clear, definite, and unmistakable. When something shows a decided difference, you can't miss it. A student who was struggling with fractions but suddenly understands them has made decided progress. A recipe that calls for a decided preference for sweetness over sourness isn't asking for a subtle hint of sugar.

The word suggests that something stands out so clearly that there's no room for doubt or confusion. If your friend has a decided advantage in chess because she's been practicing every day, that advantage is obvious to everyone watching. When a judge makes a decided ruling, the decision is firm and final, not wishy-washy or uncertain.

You might also see decided used to describe someone's manner or attitude. A person with decided opinions knows what they think and states it confidently. Someone who speaks in a decided tone isn't mumbling or hedging. They're clear and direct.

The related word decidedly works as an intensifier, meaning “definitely” or “without question.” If one mountain trail is decidedly harder than another, there's no debate about which one requires more effort.