Novel, one we both know well (3,6,6)
I believe the answer is:
our mutual friend
I believe this is a double definition.
'novel' is the first definition.
(I've seen this before)
'one we both know well' is the second definition.
(Other definitions for our mutual friend that I've seen before include "John Harmon" , "someone we both know" , "you and I know and like" , "Novel" , "China we share" .)