Fourth Estate prepared for exercise (5-2)
I believe the answer is:
press-up
'exercise' is the definition.
(I've seen this before)
'fourth estate prepared' is the wordplay.
'fourth estate' becomes 'press' (term for the press).
'prepared' becomes 'up' (similar in meaning).
'press'+'up'='PRESS-UP'
'for' acts as a link.
(Other definitions for press-up that I've seen before include "Face-to-the-floor exercise" , "Form of arm exercise" , "Arm exercise while lying face down" , "Keep-fit exercise" , "PE exercise" .)