Release son caught by a foreign section on the way back (7)
I believe the answer is:
unstrap
'release' is the definition.
(thesaurus)
'son caught by a foreign section on the way back' is the wordplay.
'son' becomes 's'.
'caught by' is an insertion indicator.
'a foreign' becomes 'un' ('a' translated into French).
'section' becomes 'part' ('part' can be a synonym of 'section'**).
'on the way back' says the letters should be written backwards.
'part' back-to-front is 'trap'.
'un'+'trap'='untrap'
's' put into 'untrap' is 'UNSTRAP'.
(Other definitions for unstrap that I've seen before include "loose" , "Loosen tie" , "Release" , "Remove fastenings from" .)