- adjective referring to something with physical properties which are different according to direction, e.g. non-symmetrical crystals with different dimensions or refractive indices along each of two or more axes
- In construction, a term to describe materials like wood that exhibit different properties when measured along different axes.
- Having physical properties that vary depending on the axis along which they are measured. For example, the index of refraction of a substance may display this phenomenon. This contrasts with isotropic, in which physical properties are identical in all directions. Also known as aelotropic.