Subject of story gets reduced by 50% (5)
I believe the answer is:
liege
'subject' is the definition.
(thesaurus)
'story gets reduced by 50' is the wordplay.
'story' becomes 'lie' (I've seen this before).
'gets' says to put letters next to each other.
'reduced by 50' becomes 'ge' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'lie'+'ge'='LIEGE'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for liege that I've seen before include "Loyal vassal" , "European city" , "European university" , "Belgian city or feudal superior" , "Subject in history" .)