Epitome of precision - ain't disorganised (15)
I believe the answer is:
personification
'epitome' is the definition.
(thesaurus)
'of precision ain't disorganised' is the wordplay.
'disorganised' indicates an anagram.
'of'+'precision'+'aint'='ofprecisionaint'
'ofprecisionaint' with letters rearranged gives 'PERSONIFICATION'.
(Other definitions for personification that I've seen before include "John Bull, say" , "representation" .)