What are the correct names for the two faces of an airfoil?
You can call the two opposite sides suction side (for face on the convex side of the camber curve) and pressure side (for face on the concave side of the camber curve).

This has been used in a number of cases- for example in NASA Report CR-1767 Section Data for Thin, Highly Cambered Airfoils in Incompressible Flow:


  .. flow separation on the pressure side at negative incidence angles and on the suction side at positive incidence angles. 


for airfoils and in National Energy Technology Laboratory Handbook:


  The airfoils are curved, convex on one side and concave on the other, with the rotor rotating toward the concave side. The concave side is called the pressure side of the blade, and the convex side is called the suction side of the blade.  


for compressor blades.