- window glass made in flat, circular plates by blowing and whirling, with a small knot in the center left by the blower's rod
- a very clear optical glass with a low index of refraction
See crown glass in American Heritage Dictionary 4
- A soda-lime optical glass that is exceptionally hard and clear, with low refraction and low dispersion.
- A form of window glass made by whirling a glass bubble to make a flat circular disk with a lump left in the center by the glass blower's rod.