Thansk CC, it seems that wing Dihedral is an angle raising the centerline of the wing tip above the centerline of the wing root. It can also be expressed as a measurement of length. given this definition it seems that any curve of the wing is irrelevant as the measurement is from root to tip and alonh the horizontal - a diagram for which would produce a triangle. then wingspan * sin of the angle gives the valiue for dihedral. If i come across the question in the exams i think i will go with - "Gives lateral stability"
Thanks for your input.