The Collaborative International Dictionary of English v.0.48:
Brachydiagonal \Brach`y*di*ag"o*nal\, a. [Gr. brachy`s short + E. diagonal.] Pertaining to the shorter diagonal, as of a rhombic prism. [1913 Webster] Brachydiagonal axis, the shorter lateral axis of an orthorhombic crystal. [1913 Webster]The Collaborative International Dictionary of English v.0.48:
Brachydiagonal \Brach`y*di*ag"o*nal\, n. The shorter of the diagonals in a rhombic prism. [1913 Webster]