Key in front of trap splitting Frenchman turned (5)
I believe the answer is:
enter
'key in' is the definition.
(both can mean to type in with a keyboard)
'front of trap splitting frenchman turned' is the wordplay.
'front of' says to take the initial letters.
'splitting' indicates putting letters inside.
'frenchman' becomes 'rene' (common French name).
'turned' shows that the letters should be reversed in order.
The initial letter of 'trap' is 't'.
't' going within 'rene' is 'retne'.
'retne' backwards is 'ENTER'.
(Other definitions for enter that I've seen before include "Take part in a contest" , "Get in" , "Come in - register" , "Pierce" , "Move into" .)