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The Collaborative International Dictionary
Macropinacoid

Macropinacoid \Mac`ro*pin"a*coid\, n. [Macro- + pinacoid.] (Crystallog.) One of the two planes of an orthorhombic crystal which are parallel to the vertical and longer lateral (macrodiagonal) axes.

Wiktionary
macropinacoid

n. One of the two planes of an orthorhombic crystal which are parallel to the vertical and longer lateral (macrodiagonal) axis.