This lets me out (4)
I believe the answer is:
exit
'out' is the definition.
(I've seen this in another clue)
'this lets me' is the wordplay.
I cannot quite see how this works, but
'me' could be 'i' and 'i' is found within the answer.
The remaining letters 'ext' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for exit that I've seen before include "Relinquish the lead" , "Means of egress" , "Depart" , "Way to go!" , "Way out sign" .)