Hello, I found this on the net, might help: "in order to make the segmentation of words into smaller parts a little clearer, we differentiate between the base, the stem and the root of a word in morphological terms. base: reactions stem: reaction (s) root: (re) act (ion) (s) [The base is a morpheme or morphemes regarded as a form to which affixes or other bases may be added.]The stem is the base with all inflectional suffixes removed, whereas the root is what remains after all affixes have been taken off. When doing computational text analysis stemming (i.e. removing all inflectional endings) is frequently undertaken in order to avoid counting different word forms (e.g. house and houses) as separate words.

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