Lighter study for the tomboy (6)
I believe the answer is:
hoyden
'the tomboy' is the definition.
('hoyden' can be a synonym of 'tomboy')
'lighter study' is the wordplay.
'lighter' becomes 'hoy' (synonyms).
'study' becomes 'den' (term for a study or office).
'hoy'+'den'='HOYDEN'
'for' is the link.
(Other definitions for hoyden that I've seen before include "Reliable (convict)" , "A boisterous girl" , "No Hyde (anag)" , "A girl who behaves in a boyish manner" , "Romp" .)