The correct girth, maybe (5)
I believe the answer is:
right
'the correct' is the definition.
(right can mean correct)
'girth maybe' is the wordplay.
'maybe' indicates anagramming the letters.
'girth' with letters rearranged gives 'RIGHT'.
(Other definitions for right that I've seen before include "Morally correct" , "It's what you deserve" , "licence" , "Due" , "Accurate" .)