Am. heritage dict. (Copter: informal, a Helicópteros)

Web. 3 (Airplane: a fixed-wing aircraft heavier than air that is driven by a screw propeller or a high velocity jet and supported by the dynamic reaction of the air against its wings; helicopter: an aircraft whose support is the air is derived chiefly from the aerodynamic forces acting on one or more roters turning about substantially vertical axes)

Comments concerning NPRM 49' CFR 830 from Sikorsky Aircraft Corporation web site, Jan. 24, 2006 (The analogy that NTSB draws is not correct: helicopters are not airplanes, and have distinct and obvious differences)