A card or a letter? (9)
I believe the answer is:
character
I believe this clue is a double definition.
'a card' is the first definition.
(thesaurus)
'a letter?' is the second definition.
(letter is a kind of character)
'or' is the link.
(Other definitions for character that I've seen before include "case" , "Type - letter" , "card" , "Letter or number" , "Part" .)