It is shown that, in tokamak plasmas, finite drift/banana-orbit width (FOW) effects play crucial roles in the nonlinear evolution of kinetic/geodesic acoustic modes (KGAM/GAM). In particular, it is found that, in contrast to the negligible second-harmonic generation, KGAM/GAM can generate appreciable zero-frequency zonal flow (ZFZF) due to the FOW effects. On the other hand, ZFZF is found to have negligible effects on the dynamics of GAM/KGAM. This route of generating ZFZF has important implications to the nonlinear dynamics of zonal flows and, consequently, drift wave turbulences. © CopyrightEPLA, 2014.