Source : Webster's Revised Unabridged Dictionary (1913)

Stemmer \Stem"mer\, n.
   One who, or that which, stems (in any of the senses of the
   verbs).

Source : WordNet®

stemmer
     n 1: a worker who strips the stems from moistened tobacco leaves
          and binds the leaves together into books [syn: {stripper},
           {sprigger}]
     2: a worker who makes or applies stems for artificial flowers
     3: an algorithm for removing inflectional and derivational
        endings in order to reduce word forms to a common stem
        [syn: {stemming algorithm}]
     4: a miner's tamping bar for ramming packing in over a blasting
        charge
     5: a device for removing stems from fruit (as from grapes or
        apples)

Source : Free On-Line Dictionary of Computing

stemmer
     
         A program or {algorithm}
        which determines the morphological root of a given inflected
        (or, sometimes, derived) word form -- generally a written word
        form.
     
        A stemmer for English, for example, should identify the
        {string} "cats" (and possibly "catlike", "catty" etc.) as
        based on the root "cat", and "stemmer", "stemming", "stemmed"
        as based on "stem".
     
        English stemmers are fairly {trivial} (with only occasional
        problems, such as "dries" being the third-person singular
        present form of the verb "dry", "axes" being the plural of
        "ax" as well as "axis"); but stemmers become harder to design
        as the morphology, orthography, and {character encoding} of
        the target language becomes more complex.  For example, an
        Italian stemmer is more complex than an English one (because
        of more possible verb inflections), a Russian one is more
        complex (more possible noun declensions), a Hebrew one is even
        more complex (a {hairy} writing system), and so on.
     
        Stemmers are common elements in {query} systems, since a user
        who runs a query on "daffodils" probably cares about documents
        that contain the word "daffodil" (without the s).
     
        ({This dictionary} has a rudimentary stemmer which currently
        (April 1997) handles only conversion of plurals to singulars).
     
        (1997-04-09)