A cross-classification of less importance to the grammar is that of monomorphemic words (i.e. free morphemes) and polymorphemic words. Monomorphemic words may be members of a paradigm of variables [...], and many polymorphemic words are invariable (not members of a paradigms: e.g. "without, midway"). Polymorphemic words and bases include some constituent morphemes that are irrelevant to the grammatical class of the whole and do not of themselves carry any grammatical category or limitation.
- Robins (2004), Pag. 140