Lattice dynamics of the ordered gamma -ZrH phase was studied by inelastic neutron scattering (INS). It was found that the hydrogen optical peak in the INS spectrum had three maxima at energy transfers of 141.5, 148.7 and 156.3 meV. The peak was accurately described using the Born-von Karman model. Anharmonicity of hydrogen vibrations was evident in the high-energy range of the spectrum from a strong sharp peak at E=269.7 meV and broader features below the bands of free-multiphonon scattering. These anharmonic phenomena were attributed to the bound multiphonon states (biphonon, triphonon, tetraphonon and their combinations), and the values of the binding energies of biphonons and triphonons were obtained from the experimental data.