Mean couple one’s escaped from (3)
I believe the answer is:
par
'mean' is the definition.
(I've seen this before)
'couple one's escaped from' is the wordplay.
'couple' becomes 'pair' (synonyms).
'one' becomes 'i' (Roman numeral).
'escaped from' is a deletion indicator.
'pair' with 'i' removed is 'PAR'.
(Other definitions for par that I've seen before include "Average - equality" , "Average standard" , "Median" , "State of equality" , "standard for course" .)