A thick airfoil shape that is to form a blade neck for blades, the blade neck connecting a blade root to a streamlined portion of the blade, and/or a blade cuff connecting a blade to the hub of an aircraft rotor. The thick airfoil shape has a leading edge and a trailing edge together with thick airfoil profiles for which the particular positions of points defining the maximum thickness of each airfoil profile make it possible to improve the aerodynamic behavior of the thick airfoil shapes and of the rotor during rotation of the rotor while the aircraft is advancing, for the blade both when it is advancing and when it is retreating. The thick airfoil shape also serves to reduce the vibration as generated by a wake from the rotor on a tail boom or a horizontal and/or vertical stabilizer of the aircraft.