'Macropinacoid' definitions:

Definition of 'Macropinacoid'

From: GCIDE

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. [1913 Webster]