Poorest journalist's material (7)
I believe the answer is:
worsted
'material' is the definition.
(I know that worsted is a type of material)
'poorest journalist's' is the wordplay.
'poorest' becomes 'worst' (similar in meaning).
'journalist' becomes 'ed' (short for editor).
'worst'+'ed'='WORSTED'
(Other definitions for worsted that I've seen before include "sort of suit?" , "Stuffed" , "Fabric made from fine smooth wool yarn" , "cloth" , "Set word (anag.)" .)