Definitions for "Anechoic"
Away from echo, i.e. absorbing
Having no reverberation. An anechoic chamber is a room in which there is no echo.
Neither having nor producing an echo angle of attack. The acute angle of attack between the chord of an airfoil and its direction of motion relative to the air, often referred to as "alpha"; when an airfoil's exceeds the one that provides maximum lift, it goes into a stall, losing air speed and, potentially, the capability of the pilot to control the airplane.