- Any of several North American or eastern Asian evergreen trees or shrubs of the genus Thuja, having flattened branchlets with opposite, scalelike leaves and small cones. They are grown as ornamentals and for timber.
- Any similar plant of the genus Platycladus or Thujopsis. Also called thuja.
- Anatomy The white nerve tissue of the cerebellum, which has a treelike outline in a median section.