We have discovered that HD 40765 is a singly periodic Delta Scuti star pulsating in the fundamental or first overtone radial mode with a period of 4.070hr. Its light variations are non-sinusoidal and have peak-to-peak amplitudes of dB = 0.21 mag and dV = 0.15 mag. This star is strongly metallic-lined. We classify the spectrum Fmp (kA7hF5mF5), where the ''p'' does not indicate peculiar in the Ap sense, but peculiar in the sense that the spectrum cannot be fully parameterised. HD 40765 is a large amplitude Rho Scuti star which is also a Rho Pup, or evolved Am, star. By comparison with Rho Puppis itself, the inferred surface radial velocity variations are 14 km/s peak-to-peak. This implies either: 1) that such pulsation can be non-turbulent at the level of predicted diffusion velocities of order cm/s , or 2) that diffusion should be reconsidered as the sole explanation for the abundance anomalies in this star.