Why a helicopter chopper?

Q: Why is a helicopter called a "Chopper"? A: I think the names comes from the sound of the blades make: whop-whop or chop-chop. FYI, the helicopters that have the loud popping of the blades are usually a 2-blade of the Bell Helicopter design. The multi-blade helicopters do not have a sound as distinctive as the Bell helicopters. The sound comes from the blade striking the vortex generated by the blade ahead of it.