A crystal system characterized by four crystallographic axes of which three are horizontal and equal in length with an angle of 120° between them, and a fourth axis which is vertical. The vertical axis is one of six-fold symmetry. The hexagonal system differs from the trigonal system, which has a vertical axis of three-fold symmetry.
Hexagonal
- Greibach normal form
- greisen
- Greisen–Zatsephin–Kuzmin limit
- Grelling’s paradox
- Grenada
- Grenville, George (1712–70)
- Grenville, Sir Richard (1542–91)
- Grenville, William Wyndham, Baron (1759–1834)
- Grenvillian orogeny
- Grenz horizon
- grenz rays
- Gresham, Sir Thomas (1519–79)
- Gresham’s law
- grey body
- grey-brown podzolic
- Grey, Charles, 2nd Earl (1764–1845)
- grey crescent
- Grey, Edward, Viscount Grey of Fallodon (1862–1933)
- greyhound
- grey importer
- Grey, Lady Jane (1537–54)
- grey level
- grey-level array
- grey-level image
- grey matter