Dreadfully means extremely or terribly, in a way that's usually bad or unpleasant. When something is dreadfully cold, it's painfully, miserably cold, far beyond just chilly. When you're dreadfully sorry about breaking your friend's favorite toy, you feel deeply and seriously sorry, far more than a little bit.

A dreadfully boring lecture doesn't just make you yawn; it feels endless and almost painful to sit through. A dreadfully difficult puzzle might frustrate you so much you want to give up.

Interestingly, people sometimes use dreadfully to intensify positive things in an ironic or old-fashioned way. A character in a classic British novel might say they're dreadfully pleased to meet you, meaning extremely pleased, though this usage sounds formal and outdated today. In most modern contexts, though, when something is dreadfully anything, it's dreadfully bad: dreadfully hot, dreadfully unfair, or dreadfully wrong.