Rewrite any incomplete clue? Madness (6)
I believe the answer is:
lunacy
'madness' is the definition.
(I know that insaneness can be written as lunacy)
'rewrite any incomplete clue?' is the wordplay.
'rewrite' indicates an anagram.
'incomplete' means to remove the last letter.
'clue' with its final letter taken away is 'clu'.
'any'+'clu'='anyclu'
'anyclu' is an anagram of 'LUNACY'.
(Other definitions for lunacy that I've seen before include "Tomfoolery" , "Extreme folly, insanity" , "Madness, insanity" , "State of madness" , "Moon madness" .)