Trial of unlimited work contract (6)
I believe the answer is:
ordeal
'trial' is the definition.
(I've seen this before)
'unlimited work contract' is the wordplay.
'unlimited' says to take the centre (discard the edges or 'limits' of the word).
'contract' becomes 'deal' (I've seen this before).
The middle of 'work' is 'or'.
'or'+'deal'='ORDEAL'
'of' acts as a link.
(Other definitions for ordeal that I've seen before include "Difficult and testing experience" , "Severe trial" , "Difficult and painful experience" , "A difficult and harrowing experience" , "A tough time or hardship" .)