Key frequently used to get in (5)
I believe the answer is:
enter
This clue could be a double definition.
'key frequently' is the first definition.
'enter' can be an answer for 'key' (key on a computer keyboard). I'm not certain of the 'frequently' bit.
'to get in' is the second definition.
('enter' can be a synonym of 'get in')
'used' is the link.
Can you help me to learn more?
(Other definitions for enter that I've seen before include "Inscribe" , "Go/come in" , "Break in" , "Register (as a competitor)" , "Record (in a log)" .)