You cannot possibly have the definition to a word. Definitions are not static -- they're dynamic!
Racism can mean one thing for you and something else for another person.
I find anyone that claims to actually KNOW the definition of any word to be just a little sanctimonious.
All you can do is argue a definition's validity by presenting factual information and attacking the premises that support your opponent's idealogy.
Merriam Webster is not a valid source for this