Is Overfitting a Word?

Wikipedia defines overfitting as occurring when a model describes random error or noise instead of the underlying relationship. And, yet, as I write this, the Blogger editor is telling me that "overfitting" is a spelling error. Shouldn't a nontrivial Wikipedia page be enough to confirm that "overfitting" is, in fact, a correct spelling? 'course, I know from experience that this sort of question is easy to state but difficult to resolve properly...