Press your first piece of sarcasm (5)
I believe the answer is:
irony
'sarcasm' is the definition.
(I know that sarcasm can be written as irony)
'press your first piece' is the wordplay.
'press' becomes 'iron' (ironing is a kind of pressing).
'first piece' says to take the initial letters.
The initial letter of 'your' is 'y'.
'iron'+'y'='IRONY'
'of' acts as a link.
(Other definitions for irony that I've seen before include "type of discussion, originally" , "What "as clear as mud" demonstrates" , "the reverse of what you'd expect" , "Satirical speech form" , "Socratic method of discussion" .)