Meroherdal relates to the crystallographic symmetry of crystals, specifically used to describe crystallographic twins that share a common unit cell. Some synonyms for meroherdal include partial-merohedral, sub-merohedral, and quasi-merohedral. These terms are all used to describe twinned crystals that share some facets and symmetry elements but not all. Another possible synonym is pseudomerohedral, which describes a crystal that appears to be merohedral but is actually only partially twinned. Anatropous is another term that can be used to describe a particular type of meroherdal twinning where the two parts of the twin are related by a two-fold axis of rotation.