Sarcasm not finished in press (4)
I believe the answer is:
iron
'press' is the definition.
(I know that press can be written as iron)
'sarcasm not finished' is the wordplay.
'sarcasm' becomes 'irony' (synonyms).
'not finished' means to remove the last letter.
'irony' with its final letter taken away is 'IRON'.
'in' is the link.
(Other definitions for iron that I've seen before include "Heavy metal that rusts easily" , "inflexible > club" , "See 14" , "Main part of steel" , "The one who was 'not for turning'" .)