What does "vitreous" mean?

Vitreous: Of or pertaining to glass; derived from glass; as, vitreous electricity. Vitreous body (Anat.), the vitreous humor. See the Note under Eye. -- Vitreous electricity (Elec.), the kind of electricity excited by rubbing glass with certain substances, as silk; positive electricity; -- opposed to resinous, or negative, electricity. -- Vitreous humor. (Anat.) See the Note under Eye. -- Vitreous sponge (Zoöl.), any one of numerous species of siliceous sponges having, often fibrous, glassy spicules which are normally six-rayed; a hexactinellid sponge. See Venus's basket, under Venus.