A stem, by definition, belongs to some part of speech. In the case of a simple stem, its part of speech is simply one of the facts about the morpheme. In the case of a derived stem, however, the part of speech to which it belongs can often be predicted in terms of one or another of its ICs. This is especially true in the case of forms built with derivational affixes.
- Hockett (1958), a pag.243

When all inflectional affixes are stripped from a word, what is left is a ‘stem’. In some cases the stem itself occurs as a complete word, as in English ‘boys’, where stripping the inflectional affix ‘–s’ “plural” from the word leaves just the singular form ‘boy’. In such cases, it is convenient to distinguish between mention of the stem and mention of the morphemically identical whole word by writing the former with a hyphen: ‘boy-’ but ‘boy’. In other cases the stem is a bound form.
- Hockett (1958), a pag.209-210