What does "jack-fool of a brother Ambrose" mean?
It is true also that I did lay my hands upon this jack-fool of a brother Ambrose, though, as you can see, I did him little scathe.
(The White Company, Arthur Conan Doyle)
scathe : (noun) The act of damaging something or someone.
Jack-fool: (noun) A fool
Ambrose : immortal