[...] a root is defined with respect to a lexeme, while a stem is always defined with respect to a realization rule. One might say that "root" thus abstracts away from all morphology. The most important thing about roots, in the sense for which I wish to reserve the term, is that they be morphologically unanalyzable. A root is what is left when all morphological structure has been wrung out of a form.
- Aronoff (2004), a pag.57