(usually uncountable) An amorphous solid, often transparent substance, usually made by melting silica sand with various additives (for most purposes, a mixture of soda, potash and lime is added).

(countable, uncountable, by extension) Any amorphous solid (one without a regular crystal lattice).

(countable) A vessel from which one drinks, especially one made of glass, plastic, or similar translucent or semi-translucent material.

(metonymically) The quantity of liquid contained in such a vessel.

(uncountable) Glassware.

A mirror.

A magnifying glass or telescope.

(sports) A solid, transparent material used as a barrier, also referring to the backboard in basketball and the protective screen in ice hockey.

A barometer.

(attributive, in names of species) Transparent or translucent.

(uncountable, photography, informal) Lenses, considered collectively.

(now rare) A pane of glass; a window (especially of a coach or similar vehicle).

(transitive) To fit with glass; to glaze.

(transitive) To enclose in glass.

(transitive) Clipping of fibreglass. To fit, cover, fill, or build, with fibreglass-reinforced resin composite (fiberglass).

(transitive, UK, colloquial) To strike (someone), particularly in the face, with a drinking glass with the intent of causing injury.

(transitive, science fiction) To bombard an area with such intensity (nuclear bomb, fusion bomb, etc) as to melt the landscape into glass.

(transitive) To view through an optical instrument such as binoculars.

(transitive) To smooth or polish (leather, etc.), by rubbing it with a glass burnisher.

(transitive) To make glassy.

(intransitive) To become glassy.