What is "diglyph"

Diglyph \Di"glyph\, n. [Gr. ?; di- = di`s- twice + ? to hollow out, carve.] (Arch.) A projecting face like the triglyph, but having only two channels or grooves sunk in it.

n. A member with two vertical channels or grooves, without the two lateral half grooves which characterize the triglyph.