Save key found in French street (6)
I believe the answer is:
rescue
'save' is the definition.
(rescuing is a kind of saving)
'key found in french street' is the wordplay.
'key' becomes 'esc' ('Escape' key on a computer keyboard).
'found in' is an insertion indicator.
'french street' becomes 'rue' (French for street or road).
'esc' placed into 'rue' is 'RESCUE'.
(Other definitions for rescue that I've seen before include "Save from harm" , "Salvage" , "saving" , "Extricate" , "Deliver from harm" .)