The Collaborative International Dictionary of English v.0.48:
Stem \Stem\, v. t. [imp. & p. p. Stemmed; p. pr. & vb. n.
Stemming.] [Either from stem, n., or akin to stammer; cf.
G. stemmen to press against.]
To oppose or cut with, or as with, the stem of a vessel; to
resist, or make progress against; to stop or check the flow
of, as a current. "An argosy to stem the waves." --Shak.
[They] stem the flood with their erected breasts.
Stemmed the wild torrent of a barbarous age. --Pope.
The Free On-line Dictionary of Computing (30 December 2018):
A program or algorithm
which determines the morphological root of a given inflected
(or, sometimes, derived) word form -- generally a written word
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).