The boys at Oxford University Press attoned somewhat for their sins when they published Hanks & Hodges massive tome: *A Dictionary of Surnames*. "Wyndham" is in that, but I didn't use their interpretation of the name because it sounded a bit convoluted.
Instead I turned to my old favorite, Elsdon C. Smith (former president of the American Name Society and member of the International Committee of Onomastic Sciences), and his *New Dictionary of American Family Names*. The esteemed Mr. E.C. Smith is (at least as far as I'm concerned) the last word on last names.
-- Nanaea