Cannibal tidier after mat trimmed (8)
I believe the answer is:
maneater
'cannibal' is the definition.
(someone who eats human flesh)
'tidier after mat trimmed' is the wordplay.
'tidier' becomes 'neater' ('neat' can be similar in meaning to 'tidy').
'after' is a charade indicator (letters next to each other).
'trimmed' means to remove the last letter (the final letter is trimmed off).
'mat' with its final letter removed is 'ma'.
'neater' after 'ma' is 'MANEATER'.
(Other definitions for maneater that I've seen before include "Highly-sexed, domineering woman" , "Tiger, say" , "Vamp" , "Voracious woman!" .)