Relax -- peacekeepers working following strike (8)
I believe the answer is:
Here is my best explanation:
'relax' is the definition.
Although both the answer and definition are verbs in their base form, I can't see how one could define the other.
'peacekeepers working following strike' is the wordplay.
'peacekeepers' becomes 'un'.
'working' becomes 'on'.
'following' is a charade indicator (letters next to each other).
'strike' becomes 'butt' (butting is a kind of striking).
'on' put after 'butt' is 'button'.