Strong quasielastic features have been found in light scattering from diamond in the frequency range 0 to \ifmmode\pm\else\textpm\fi{} 200 GHz and have been investigated as a function of wave-vector transfer ($Q$) and temperature ($T$). The evolution of a relatively narrow Lorentzian component (\ensuremath{\sim} 10 GHz) demonstrates for the first time the manner in which a two-phonon difference spectrum in the collision-free regime (low $T$ and large $Q$) develops into entropy-fluctuation scattering in the collision-dominated regime (high $T$ and low $Q$).