Joint titleholder (8)
I believe the answer is:
namesake
'joint titleholder' is the definition.
The definition suggests a singular noun which matches the answer.
This is the entire clue.
(Other definitions for namesake that I've seen before include "The PM is of George Orwell" , "One's similarly entitled" , "What one may be called" , "Person with the identical monicker" , "one similarly entitled" .)