Using a light-beating technique for an appropriate scattering geometry, we have measured the bend orientational diffusivity (D-bend) for an "hexa-n-alcanoyloxytruxene" (HATXC(12)H(25)) sample which exhibits a disk-like thermotropic nematic phase (N-D) between 57 degrees C and 84 degrees C. From K-33 measurement by the Frederiks method, the bend viscosity (eta(bend)) is deduced. It is about 100 times higher than those corresponding to rod-like thermotropic nematics. From previous measurements of D-splay and D-twist for HATXC(12)H(25), we have deduced the elastic constants (K-11;K-22) and the viscosities (eta(splay),eta(twist)). It has been concluded that, although there is a difference between the two kinds of molecules (disk-like and rod-like), the backflow has the same effect as in rod-like nematic phase.