Open the door to the French element (3,2)
I believe the answer is:
let in
'open the door to' is the definition.
(I've seen this in another clue)
'the french element' is the wordplay.
'the french' becomes 'le' ('the' in French).
'element' becomes 'tin' (tin is a kind of element).
'le'+'tin'='LET IN'
(Other definitions for let in that I've seen before include "Grant entry" , "Allow to enter" , "Allowed to enter" , "Admit" , "swindle . . ." .)