It has been conjectured that the name is an Arabic modification of adnoun, and that again derived from Ad nonum, meaning the ninth Roman mile from Tyre; but as far as my memory serves me, that does not correspond with the real distance.
"Byeways in Palestine"
James Finn
188. "adnoun, or Adjective, comes from the Latin, ad and jicio, to add to."
"The Grammar of English Grammars"
Goold Brown