1. Colourless glass made of almost pure silica
   - quartz glass, quartz, lechatelierite, crystal

Type of: natural glass

• otherworldly
• Othman I
• Otho
• Otho I
• Otho of Lagery
• othonna
• otic
• otic ganglion
• Otides
• Otididae
• otiose
• otiosity
• Otis
• Otis Skinner
• Otis tarda
• otitis
• otitis externa
• otitis interna
• otitis media
• Oto
• Otoe
• otoganglion
• OTOH
• otolaryngologist
• otolaryngology