My 1961 copy of Webster’s New Collegiate Dictionary defines Kantianism thusly:

Kant′i·an·ism (-iz’m)
n. The philosophy of Immanuel Kant (1724–1804). He held that the mind furnished the forms of experience and the sense organs furnish only impressions. Our knowledge is therefore only subjective. But Kant shows the necessity of a belief in God, freedom, and immortality, if we are to have the institutions of civilization. And he further shows that without the a priori idea of intelligent design in nature we could not recognize any phenomena of life in plants or animals or other organisms.

Now, it has been more than 6 years since read much Kant, and I shouldn’t be considered an expert in anything, so I’m not in much of a position to critique the accuracy of the content of that definition. Certainly, the first half is reasonable, and I seem to recall him saying some things in Der Einzig Mögliche Beweisgrund… that could be understood to mean something like the second half of the definition. I’d even be willing to say that the definition reflects a familiarity with Kantian philosophy about as well as any 5-sentence summary could hope to do. What bothers me is the “But.” Without that little conjunction (that fails, I might add, to conjoin anything), the definition would present a (possibly imbalanced) survey of major themes and ideas Kant dealt with, presumably what one might hope to find in a dictionary. But the “But” transforms the definition into an exegesis, or an editorial, or perhaps an apology of Kantian philosophy, which I would never hope to find in a dictionary.

A more recent (and concise) definition from our friend Webster may be found at dictionary.reference.com.

NP: Sinead O’Connor, Just Like U Said It Would B