Types of Definitions
There are different types of definitions. One type tries to describe how a word is typically used. The New Oxford American Dictionary is filled with these. Since they describe the standard way a word is used, I will call them standard definitions.
A second type specifies the meaning of a word within a particular context. Since these definitions only apply to their local context, I will call them local definitions.
Local definitions have several uses. They can reduce repetition. For example, a legal contract may repeat the phrase “a natural person, partnership, corporation, estate, trust, or any legal entity” many times. By defining person to mean “a natural person, partnership, corporation, estate, trust, or any legal entity,” the contract is shortened. Unlike a standard definition, the contract’s definition makes no claim about how person is usually used. It only tells the reader to equate person with this phrase while reading the contract.
Local definitions are meant to simplify a contract without affecting its meaning. Whether a local definition accomplish this depends on how often it is used. Two uses likely isn’t enough to justify making the reader keep it in mind while reading. Ten uses likely is enough since you have shortened ten sentences. Furthermore, local definitions let the reader to separate the cognitive load of understanding a definition from understanding the sentences it occurs in. (Local definitions also help lawyers write and update contracts.)
Local definitions are also used in less formal contexts, although less explicitly. For example, an author may state, near the end of chapter two, their own definition of racism. As in a contract, the rest of the book must be read with this definition substituted for the standard one. But unlike contract lawyers, authors may hope their definitions become standard.
Local definitions, especially ones that redefine words, can cause confusion. Quotations are easily misunderstood if an unaware reader substitutes the standard definition for the author’s intended local one. This confusion can be avoided by using new words, or by using longer, more precise phrases, instead. But both alternatives have shortcomings. New words are hard to remember, and phrases get tiresome. The latter problem may be evident in my use of the phrases local definition and standard definition.
A local definition can’t be wrong. It can only be useless—too precise, too general, or too confusing. Words that are too specific to be useful for most of us, may be useful for specialists. Sailors will need nautical terms and botanists botanical ones.
A standard definition, on the other hand, can be wrong if it’s not what people usually mean by the word. Language purists may have other reasons why a definition is wrong, but I think they’re usually born out of frustration that standard definitions can shift over time.
These language shifts are one reason that Shakespeare is hard to understand. It is also one reason it is hard to know what people usually mean. Word use also varies geographically, which is why there are British dictionaries and American dictionaries. Even two same-aged Americans will use words differently.
Despite these complexities, whether a standard definition is correct is a question of averages. What does the average American mean when they use racism? This question is hard, but not impossible, to answer. To do so, dictionary writers collect billions of American sentences to analyze how, and how often, words are used in them. They also track how word use changes and update their definitions accordingly.
Sometimes words have competing definitions. This can occur for political reasons, but it is also common among academics. Ten out of fifteen of the professors in a niche prefer one definition and the other five another. When they publish, local definitions are given to avoid confusion. “I’m using Johnston’s definition of the word.” Nobody outside their niche needs such a specific word, so nobody else cares.