A great American author or two (5)
I believe the answer is:
twain
I believe this is a double definition.
'a great american author' is the first definition.
(Mark Twain, 1835-1910)
'two' is the second definition.
(archaic term for 'two')
'or' is the link.
(Other definitions for twain that I've seen before include "Two of the same kind, archaically" , "Mark, say" , "Two items of the same kind and well-known author" , "I want (anag) - US novelist and humorist" , "A number in company" .)