Revising definitions is an important part of the job. A revised definition reflects the most current usage of the word. Such revisions reflect fluctuating meaning, however, not difficulty in defining.

What's easy to define? Nouns and verbs, particularly objects and action verbs. Adjectives and adverbs are probably slightly more difficult since their meanings are generally made clear by the contexts in which they appear, though perhaps highlighting the difference in nuance between closely related words (like huge and immense, or lie and deceive) is one of the trickier aspects of defining.

Less easy are abstract nouns (joy, effervescence, chaos), those describing ideas or concepts. Prepositions (in, about, with) are often a challenge to define because they describe relationships, which are practically impossible to express in words without using other prepositions.

Colors are a category of words that are traditionally difficult to define. There are two strategies commonly used by lexicographers for defining colors, and neither is ideal: 1) defining them by their relationships to other colors; or 2) defining them by using examples of things from nature that usually sport that color.

The "controversial" words (curse words, epithets, and words regarded as markers of poor English, such as ain't) are not necessarily difficult to define. Most of what makes them controversial are protestations from certain sectors of the public that such words should not be entered in the dictionary to begin with, or that they should be marked with labels that may dissuade their usage. If a word is likely to be encountered, then its definition must be in the dictionary, but usage information is also given to make the context and register of such a word very clear.