Diptych pronounced diptik is derived from the latin word diptycha and from the Greek work diptukha, di - double pitukha means fold.
In terms of paintings it is a work of art in two parts, a collective work of art arising from human creativity.
I have seen many works of art dating back to the Reneaissance period and the XIII and XIV centuries at the Uffiza Gallery in Florence, Italy. This collection of the finest italian art pieces have a collection of altar pieces done in diptych and triptych, depicting the Madonna, Jesus Christ and many other biblical representations. On seeing the placements and the continuity despite the breaks, I am in wonder of how beautiful it looks put together.
I too have painted many diptych paintings and find the process very creative and it renders the breaking of the form and creating a juxtapostion which not only is visually appealing but intrigues the viewer. It feels as though you make a break in the first part and take off at a different tangent or angle in the next part all along keeping the continuity. A creative process for an artist!!