1. The finest kind of window-glass.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• xrown glass,
• vrown glass,
• frown glass,
• drown glass,
• ceown glass,
• cdown glass,
• cfown glass,
• ctown glass,
• c5own glass,
• c4own glass,
• criwn glass,
• crkwn glass,
• crlwn glass,
• crpwn glass,
• cr0wn glass,
• cr9wn glass,
• croqn glass,
• croan glass,
• crosn glass,
• croen glass

The adjective form of the phrase "crown glass" would simply be "crown-glass".

The plural form of "crown glass" is "crown glasses".

The singular form of the word "crown glass" is "crown glass". The word "crown" itself is a noun, and "glass" functions as an adjective modifying it. Therefore, the singular and plural forms remain the same.