Finish off spell as cleaner (4)
I believe the answer is:
char
'cleaner' is the definition.
(I've seen this before)
'finish off spell' is the wordplay.
'finish off' means to remove the last letter.
'spell' becomes 'charm' (I've seen this before).
'charm' with its last letter taken off is 'CHAR'.
'as' is the link.
(Other definitions for char that I've seen before include "toast far too much?" , "Person who cleans" , "Scorch: trout-like fish" , "(Work as a) cleaner" , "Daily cleaner; burn" .)