Sensational act clears up messes (11)
I believe the answer is:
spectacular
'sensational' is the definition.
(I've seen this in another clue)
'act clears up messes' is the wordplay.
'messes' indicates an anagram (I've seen 'mess' mean this).
'act'+'clears'+'up'='actclearsup'
'actclearsup' with letters rearranged gives 'SPECTACULAR'.
(Other definitions for spectacular that I've seen before include "Visually astounding" , "Very striking or dramatic" , "Impressive, striking" , "Sensational in appearance" , "Extravaganza" .)