pedion
/ˈpɛdɪən/ /ˈpiːdɪən/Crystallography
noun
A crystal form, shown by triclinic minerals, consisting of a single face bounded by other faces having no simple symmetrical relation to it (or to each other).
Origin
Late 19th century; earliest use found in William J. Lewis (b. 1847). From ancient Greek πεδίον a plain, a flat surface from πέδον ground, earth + -ιον, suffix forming nouns.