Definition - The part of the noun, verb, etc. that inflections are added to, i.e. that remains unchanged when inflections are added.

Example -
The word pies is created by appending s to the stem pie.

Etymology -
The word derives from the Old English stemn, which is ultimately from the PIE base *sta-, to stand.

Oxford English Dictionary -
Its first citation is from 1851 : "We refer to such stems as …."
(T. H. Key in Trans. Philol. Soc. 93)

Please comment