A planar crystallographic group or wallpaper group is a group of isometries of the plane which has a subgroup of translations that is isomorphic to ℤ2. (Compare frieze groups.)
A ‘herringbone’ wallpaper
The symmetry group of the pattern in the figure is one such wallpaper group. It contains translations and glide reflections but has no non-trivial rotational symmetry. In all there are 17 wallpaper groups (up to isomorphism).
In three dimensions there are 230 crystallographic groups and in four dimensions there are 4783.
- thrust level
- thrust-sheet-top basin
- thrust vector control
- Thuban
- Thucydides (455–c.400)
- Thue-system
- thufur
- thug
- Thule
- thulite
- thulium
- thumb
- Thumba Equatorial Rocket Launching Station
- thumb drive
- thumbnail
- thumbnail image
- Thunberg, Carl Per
- thunder
- Thunderbolt
- thundercloud
- thunderstorm
- thunk
- Thuot, Pierre Joseph (1955– )
- Thuringian
- thuringite