Block and pen belonging to the writer, not new (6)
I believe the answer is:
stymie
'block' is the definition.
(synonyms)
'pen belonging to the writer not new' is the wordplay.
'pen' becomes 'sty' (sty is a kind of pen).
'belonging to the writer' becomes 'mine' (belonging to the person writing).
'not' is a deletion indicator.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'mine' with 'n' taken out is 'mie'.
'sty'+'mie'='STYMIE'
'and' is the link.
(Other definitions for stymie that I've seen before include "Thwart, foil" , "'Hinder, obstruct (6)'" , "Snooker" , "Hinder the progress of (something)" , "Block or thwart, say a golf putt" .)