Talk informally with tramp about new book (6)
I believe the answer is:
hobnob
'talk informally' is the definition.
(I've seen this before)
'tramp about new book' is the wordplay.
'tramp' becomes 'hobo' ('hobo' can be a synonym of 'tramp').
'about' means one lot of letters goes inside another.
'new' becomes 'n'.
'book' becomes 'b'.
'hobo' enclosing 'n' is 'hobno'.
'hobno'+'b'='HOBNOB'
'with' is the link.
(Other definitions for hobnob that I've seen before include "Socialise (especially with posher people)" , "Rub shoulders (with)" , "Mix socially with the biscuit" , "Socialise familiarly" , "Associate socially with superiors" .)