solipsism [ˈsɒlɪpˌsɪzəm] n.
1.) The theory that the self is the only thing that can be known and verified.
2.) The theory or view that the self is the only reality.
Etymology: Latin solus, alone + ipse, self + -ism.
"Well. What happens when paranoid meets paranoid? A crossing of solipsisms. Clearly. The two patterns create a third: a moiré, a new world of flowing shadows, interferences..." (Gravity's Rainbow, Thomas Pynchon, 1973).