What is the "snuff box" in the wrist? The doctor says I have a tendonitis of this box.

Let's start with snuff box. Snuff is tobacco in fine powder form. It's inhaled through the nostril. Snuff is kept in a small snuffbox. It should hold just enough snuff for a day's use. The user takes just a pinch or a dip each time.

In the wrist, at the base of the thumb is the anatomical snuffbox. When you pull your thumb up as if to hitch a ride, you'll see a ridge of tendon. In fact there are two
tendons: the extensor pollicis brevis and abductor pollicis longus. When these tendons contract a small hole or indentation is formed between them. This is the anatomical snuffbox. It's just about the right size to hold a pinch of snuff.

These two tendons share a common covering or sheath. Friction between these tendons and their common sheath from repeated forceful use of the hands can cause tendonitis.