orthopinacoid
/ˌɔːθə(ʊ)ˈpɪnəkɔɪd/(also orthopinakoid) Crystallography
noun
In a monoclinic crystal: a plane parallel to the vertical axis and the orthodiagonal axis.
Origin
Mid 19th century; earliest use found in James Nicol (1810–1879), geologist. From ortho- + ancient Greek πινακ-, πίναξ pinax + -oid.