Insert key (5)
I believe the answer is:
enter
I believe this is a double definition.
'insert' is the first definition.
(I know that insert can be written as enter)
'key' is the second definition.
(key on a computer keyboard)
(Other definitions for enter that I've seen before include "Register formally as a participant" , "A key on the right" , "Gain admission" , "Infiltrate" , "Take part in a contest" .)