1. A phrase that encourages one to improve one's mood, especially when sad or discouraged. Come on, the project was not a total failure—chin up! Chin up, honey—tomorrow's another day.

2. noun The act of pulling oneself upward while holding onto a bar, as at a gym. In this usage, the phrase is often hyphenated. My arms are already shaking—how many more chin-ups am I supposed to do?