text: However, derivational affixes do not necessarily alter the lexical category; they may change merely the meaning of the base and leave the category unchanged. A prefix (write →  re-write; lord → over-lord) rarely changes the lexical category in English. The prefix un- applies to adjectives (healthy → unhealthy) and some verbs (do → undo) but rarely to nouns. A few exceptions are the derivational prefixes en- and be-. En- (replaced by em- before labials) is usually a transitive marker on verbs, but it can also be applied to adjectives and nouns to form transitive verbs: circle (verb) → encircle (verb) but rich (adj) → enrich (verb), large (adj) → enlarge (verb), rapture (noun) → enrapture (verb), slave (noun) → enslave (verb).
  When derivation occurs without any change to the word, such as in the conversion of the noun breakfast into the verb to breakfast, it's known as conversion, or zero derivation.
  Derivation that results in a noun may be called nominalization. It may involve the use of an affix (such as with employ → employee), or it may occur via conversion (such as with the derivation of the noun run from the verb to run). In contrast, a derivation resulting in a verb may be called verbalization (such as from the noun butter to the verb to butter).
  Some words have specific exceptions to these patterns. For example, inflammable actually means flammable, and de-evolution is spelled with only one e, as devolution.
  Derivation and inflection
  Derivation can be contrasted with inflection, in that derivation produces a new word (a distinct lexeme), whereas inflection produces grammatical variants (or forms) of the same word.