Half the battle is getting it the heading (5)
I believe the answer is:
title
'the heading' is the definition.
(title is a kind of heading)
'half the battle is getting it' is the wordplay.
'half the' indicates taking half.
'is getting' means one lot of letters goes inside another.
'battle' halved is 'tle'.
'tle' placed around 'it' is 'TITLE'.
(Other definitions for title that I've seen before include "Mr or Mrs, say" , "inscription" , "Lord, sir, doctor etc." , "Appellation of rank" , "Name of book, picture or rank" .)