In linguistics, a word stem is a part of a word responsible for its lexical meaning. Typically, a stem remains unmodified during inflection with few exceptions due to apophony (for example in Polish, miast-o ("city") and w mieść-e ("in the city"); in English, sing, sang, and sung, where it can be modified according to morphological rules or peculiarities, such as sandhi)
Uncovering and analyzing cognation between word stems and roots within and across languages has allowed comparative philology and comparative linguistics to determine the history of languages and language families.[1] The term is used with slightly different meanings depending on the morphology of the language in question. In Athabaskan linguistics, for example, a verb stem is a root that cannot appear on its own and that carries the tone of the word.