Why arson is wrong about the end of June (6)
I believe the answer is:
reason
'why' is the definition.
(I've seen this in another clue)
'arson is wrong about the end of june' is the wordplay.
'is wrong' is an anagram indicator.
'about' indicates putting letters inside.
'the end of' says to take the final letters.
The last letter of 'june' is 'e'.
'arson' anagrammed gives 'rason'.
'rason' placed around 'e' is 'REASON'.
(Other definitions for reason that I've seen before include "Explanation for some event" , "Cause; mind's power" , "Motivation or cause" , "Explanation or motive" , "Cause; think logically" .)