the dictionary says...

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 Concise - 8th Ed. 1992

1 each of the major divisions of humankind, having distinct physical characteristics.
2 a tribe, nation, etc. regarded as of a distinct ethnic stock.
3 the fact or concept of division into races (discrimination based on race).
1a a belief in the superiority of a particular race; prejudice based on this
b antagonism towards other races, esp. as a result of this
2 the theory that human abilities etc. are determined by race.

Oxford makes no distinction between racialism and racism.

Random House Webster's College - 1991

1 a group of persons related by common descent or heredity
2 Anthropol. a classification of modern humans, sometimes esp. formerly, based on an arbitrary selection of physical characteristics as skin color, facial form, or eye shape, and now frequently based on genetic markers as blood groups
b. a human population partially isolated reproductive from other populations, whose members share a greater..
1. a belief or doctrine that inherent differences among the various human races determine cultural or individual achievement, usu. involving the idea that one's own race is superior.
2. a policy, system of government, etc. based on such a doctrine.
3. hatred or intolerance of another race or other races.

American College Dictionary - 1953

1. a group of persons connected by common descent, blood or heredity.
2. a population so connected.
3. Ethnol. a subdivision of a stock, characterized by a more or less unique combination of physical traits which are transmitted in descent
4. a group of tribes or peoples forming an ethnic stock
5. the state of belonging to a certain ethnic stock
1. a belief that human races have distinctive make-ups that determine their respective cultures, usually involving the idea that one's own race is superior and has the right to rule others.
2. a policy of enforcing such asserted right
3. a system of government and society based on it.