Won't is the shortened form of “will not.” When you say “I won't eat my vegetables,” you're declaring that you will not do it. When your friend says “I won't tell anyone your secret,” she's promising not to share what you told her.

This contraction packs determination into one syllable. There's a firmness to won't that makes it stronger than simply saying “I don't want to.” Saying “I won't give up” means you've decided: no matter what happens, you're going to keep trying. A stubborn person who won't listen to reason has made up their mind and refuses to budge.

The word appears constantly in everyday speech. “The door won't open” means it refuses to budge, no matter how hard you push. “She won't arrive until tomorrow” tells you when not to expect her. Parents might warn “you won't like the consequences” if you keep misbehaving.

Notice how won't sounds nothing like “will not.” It is one of English's odder contractions. But that unusual sound makes it memorable and gives it punch when you need to say no with conviction.