Freshmen start with the dictionary; fools stop there. In the untold zillions of debates I have had on the subject, a frightening number of people feel all debate about race is useless because nobody agrees on a standard definition of racism and all other definitions are self-interested and therefore corrupt. So they point to the dictionary.
I don't mind so much putting this here although I personally find it a waste of time - sort of like looking up the word 'literature' and then using that definition to compare Shelley to Hemingway - but I'll cover a few bases..
It is worth pointing out while we are lexically inclined that for the most part the term racist is best used as an adjective describing the content of thought rather than as a pejorative noun. practically speaking, most Americans will more readily admit to holding racist ideas than to being a racist. However subtle the difference, it is instructive.
Oxford makes no distinction between racialism and racism.