- to make (something) sharp or sharper
- sharpen a knife/pencil
- Can you sharpen the image?
- The lecture sharpened my understanding of the topic.
- The outlines of the mountains sharpened as we got closer.
- to improve (something)
- I took a course to sharpen (up) my computer skills.
- The pain suddenly sharpened.
- You'd better sharpen up if you want to keep your job.