The Collaborative International Dictionary
Orthodiagonal
Orthodiagonal \Or`tho*di*ag"o*nal\, n. [Ortho- + diagonal.] (Crystallog.) The diagonal or lateral axis in a monoclinic crystal which is at right angles with the vertical axis.
Wiktionary
orthodiagonal
n. (context crystallography English) The diagonal or lateral axis in a monoclinic crystal which is at right angles with the vertical axis.