I invited readers to think about the adjective DIOECIOUS, meaning ‘having male and female flowers on different plants’. Certainly, DIOECIOUS must be listed in any reasonably complete dictionary of English. I argued, however, that the corresponding adverb DIOECIOUSLY would not have to be listed, because both its existence and its meaning can be taken for granted once the existence of DIOECIOUS is acknowledged. This neatly illustrates the distinction between lexemes and lexical items: DIOECIOUSLY is a distinct lexeme from DIOECIOUS, since it belongs to a different word class, but it is not a distinct lexical item. This also illustrates a widespread though not universal characteristic of derivational processes: unlike inflection, they can change the word class of the bases to which they apply.

Some introductory treatments of English grammar talk as if not just many but all adverbs end in -ly. If that were true, it would be an unusual word class, all of its members being derived. In fact, simple or mono morphemic adverbs, though few in number, include some very common words (OFTEN, SELDOM, NEVER, SOON), and some other adverbs are morphologically complex without containing -ly (NOWHERE, EVERYWHERE, TODAY, YESTERDAY). Also, there are common adverbs that are formed by conversion: FAST (as in The car was driven fast) and HARD (as in They worked hard), derived from the adjective FAST (as in a fast car) and HARD (as in hard work).