Sarcasm should be limited and smooth (4)
I believe the answer is:
iron
'smooth' is the definition.
(to smooth down with an iron)
'sarcasm should be limited' is the wordplay.
'sarcasm' becomes 'irony' (synonyms).
'should be limited' means to remove the last letter.
'irony' with its last letter taken away is 'IRON'.
'and' is the link.
(Other definitions for iron that I've seen before include "Remove creases from" , "Fe - golf club" , "Heavy metal that rusts easily" , "Metal - press" , "The metallic element plays a role in the transport of oxygen by the blood" .)