Associate left with writing material (4)
I believe the answer is:
link
'associate' is the definition.
(I know that associate can be written as link)
'left with writing material' is the wordplay.
'left' becomes 'l' (common abbreviation).
'with' means one lot of letters go next to another.
'writing material' becomes 'ink' (substance for writing with).
'l'+'ink'='LINK'
(Other definitions for link that I've seen before include "Relationship; intertwine" , "Join together" , "website feature" , "Make a connection" , "Relationship; loop in a chain" .)