Common or reciprocal (6)
I believe the answer is:
mutual
I believe this clue is a double definition.
'common' is the first definition.
(synonyms)
'reciprocal' is the second definition.
(I know that reciprocal can be written as mutual)
(Other definitions for mutual that I've seen before include "like Dickens's friend?" , "Dickens novel 'Our . . . . . . Friend'" , "Reciprocal or shared, like friendship" , "Reciprocal; common" , "Joint < commonly" .)