Miss large outfit heading west (4)
I believe the answer is:
girl
'miss' is the definition.
('girl' can be a synonym of 'miss')
'large outfit heading west' is the wordplay.
'large' becomes 'l'.
'outfit' becomes 'rig' ('rig' can be a synonym of 'outfit').
'heading west' says the letters should be written backwards.
'l'+'rig'='lrig'
'lrig' written backwards gives 'GIRL'.
(Other definitions for girl that I've seen before include "Maid" , "Lassie" , "Female child" , "One of 8 [LASSES]" , "A young female" .)