Mark an old-fashioned couple? (5)
I believe the answer is:
twain
This clue might be a double definition.
'mark' is the first definition.
(Mark Twain)
'an old-fashioned couple?' is the second definition.
'twain' can be an answer for 'couple?' (archaic term for 'two'). I am not certain of the 'an old-fashioned' bit.
Can you help me to learn more?
(Other definitions for twain that I've seen before include "Mark, US writer" , "Archaic term for two" , "Old couple" , "I want (anag) - US novelist and humorist" , "Two of the same kind, archaically" .)