Domesticated cat finally made a mess (5)
I believe the answer is:
tamed
'domesticated' is the definition.
('tamed' can be similar in meaning to 'domesticated')
'cat finally made a mess' is the wordplay.
'finally' suggests the final letters.
'a mess' is an anagram indicator.
The last letter of 'cat' is 't'.
'made' anagrammed gives 'amed'.
't'+'amed'='TAMED'
(Other definitions for tamed that I've seen before include "Of animals, domesticated" , "now behaving himself?" , "Reined" , "Domesticated or subdued" .)