Cleaner scrubbing back of entrance (4)
I believe the answer is:
char
'cleaner' is the definition.
(I've seen this before)
'scrubbing back of entrance' is the wordplay.
'scrubbing back of' means to remove the last letter.
'entrance' becomes 'charm' ('charm' can be a synonym of 'entrance').
'charm' with its last letter taken off is 'CHAR'.
(Other definitions for char that I've seen before include "Drink" , "Domestic employee" , "Person who cleans" , "Partially burn; fish" , "Clean < fish" .)