Girth is the measurement around something, like the distance around a tree trunk or a person's waist. If you wrapped a tape measure around the middle of an oak tree, you'd be measuring its girth. The thicker something is, the greater its girth.

The word often describes solid, round objects. A horse's girth is measured around its barrel (the widest part of its body), and saddles need to fit properly based on that measurement. In fact, the strap that holds a saddle in place is called a girth because it wraps around the horse's body.

You might hear someone describe a massive redwood tree by its impressive girth, or talk about the girth of a ship's mast. While width measures flat distance from side to side, girth specifically means the distance around something circular or cylindrical.

When old stories describe a character of considerable girth, they're usually talking about someone quite round in the middle. It's a more formal, less direct way of describing body size than saying someone is fat or heavy.