Treacle for Missouri girls (8)
I believe the answer is:
molasses
'treacle' is the definition.
(I know that Molasses is a type of treacle)
'missouri girls' is the wordplay.
'missouri' becomes 'mo' (abbreviation for the US state).
'girls' becomes 'lasses' (lass can mean a girl).
'mo'+'lasses'='MOLASSES'
'for' acts as a link.
(Other definitions for molasses that I've seen before include "Thick dark treacle" , "Dark syrup from raw sugar" , "Thick dark syrup made from sugar cane" , "US name for treacle" , "Thick treacle left over after refining raw sugar" .)