Mark II (5)
I believe the answer is:
twain
I believe this is a double definition.
'mark' is the first definition.
(Mark Twain)
'ii' is the second definition.
(twain is a kind of ii)
(Other definitions for twain that I've seen before include "Archaic word for two" , "A number in company" , "II?" , "Two items of the same kind and well-known author" , "Pair (archaic) - US novelist, Mark" .)