Dramatist's additional matter about falsehood (7)
I believe the answer is:
moliere
'dramatist's' is the definition.
(Moliere is an example)
'additional matter about falsehood' is the wordplay.
'additional matter' becomes 'more' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'about' indicates putting letters inside.
'falsehood' becomes 'lie' (lie is a kind of falsehood).
'more' placed around 'lie' is 'MOLIERE'.
Can you help me to learn more?
(Other definitions for moliere that I've seen before include "Fr. dramatist (Tartuffe)" , "C17 French playwright (Le Misanthrope)" , "French playwright (Tartuffe)" , "Fr. comic dramatist" , "French dramatist" .)