DIY nut turned out to be messy (6)
I believe the answer is:
untidy
'to be messy' is the definition.
(synonyms)
'diy nut turned' is the wordplay.
'turned' indicates anagramming the letters.
'diy'+'nut'='diynut'
'diynut' is an anagram of 'UNTIDY'.
'out' acts as a link.
(Other definitions for untidy that I've seen before include "Disorderly and slovenly" , "Disorderly, slipshod" , "Disordered" , "Messy, not neat" , "missing order" .)