Spin-wave-based information processing provides a promising platform for low-power nanoscale computing by exploiting coherent magnon dynamics and intrinsic nonlinear interactions. A key advantage of wave-based processing for efficient miniaturization is the ability to perform operations in the frequency domain without requiring separate propagation paths for the input and output signals. Here, we demonstrate a frequency-domain spin-wave logic gate based on resonant, non-degenerate three-magnon confluence in an yttrium iron garnet nanowaveguide. Under resonant conditions, two input spin waves at different frequencies efficiently generate an output spin wave at the sum frequency, which occurs only when both input signals are present, thereby directly implementing an AND logic operation. We further show that the output intensity scales linearly with each input intensity and is therefore proportional to their product, enabling analog multiplication of two signals. These results demonstrate nonlinear magnon confluence as a versatile mechanism for frequency-domain spin-wave logic and analog signal processing.