Lexicon

A lexicon is the complete inventory of words within a language or a specific branch of knowledge. For example, a doctor uses a medical lexicon, while a sailor uses a nautical one. The term comes from the Greek word *lexikos*, which means "of or for words." In linguistics, experts view human language as having two essential parts. The first is the lexicon, which acts as a catalogue of a language's wordstock. The second is grammar, the system of rules used to combine those words into sentences.

Inside the lexicon, the individual units are called lexemes. These are not just simple, isolated pieces. Instead, lexemes contain both phonological components, which relate to sound, and morphological components, which relate to structure. To manage this complexity, researchers often use a reductionist approach. This means they try to provide a general description using as few details as possible. To organize the size of a lexicon, lexemes are grouped into lemmas. A lemma is a group of lexemes created through inflectional morphology. In a dictionary, these lemmas appear as headwords. These headwords list the necessary citation forms and any irregular forms so learners can use them correctly.

Lexicons are also organized into open and closed categories. Closed categories include words like pronouns or determiners. These rarely receive new lexemes and serve a primarily syntactic function. Open categories include nouns and verbs. These have highly active generation mechanisms and are more semantic, meaning they deal with meaning. One way a lexicon grows is through lexicalization. This is the process where new words enter the lexicon after gaining widespread usage. Sometimes, this process creates a doublet. A doublet is a pair of words, like "aptitude" and "attitude," that come from a single etymological source but have different forms.

There are several specific mechanisms used to expand a lexicon. Innovation involves the planned creation of new roots, such as through branding or slang. Borrowing occurs when a language takes words from another language. Compounding is the most common strategy across different languages. This is the process of combining lexemes to create a single new word. Sometimes, speakers use abbreviations or acronyms to shorten these compounds. For instance, "NASA" and "laser" are acronyms created by using the initial letters of a phrase.

Morphology, or the study of word structure, also plays a major role. One method is inflection, which changes a word's category, such as its tense or number. Another is derivation, which is a morphological change that results in a change of word category. For example, adding the suffix "-able" to a transitive verb creates an adjective like "readable." Another process is agglutination, where different morphemes are compounded into a single word. Even children contribute to this through neologisms. These are new word candidates that often arise from mistakes. If these neologisms gain wide usage over time, they officially become part of the lexicon.

When languages borrow words from external sources, they do so in different ways. If the language keeps the original sound and structure, it is called a guestword. If the word undergoes phonetic adaptation, it is a foreignism. If it is totally assimilated through morphemic adaptation, it is a loanword. There is also a process called phono-semantic matching. In this method, the new language uses its own words to match the sound and meaning of the source language. This can range from a close match to a simple phonetic match where only the sound is similar.

Finally, the lexicon is constantly shaped by historical forces. Comparative historical linguistics studies this evolution through a diachronic view. One force is phonological assimilation, where loanwords are modified to fit a new language's sound structure. Another is analogy, where new words follow the patterns of similar-sounding words. Metaphor can also extend the meaning of existing words. While multilingual speakers are thought to have multiple lexicons, speakers of different dialects often share one. For example, a British speaker and an American speaker both understand "ATM," even if they use different terms for a cash dispenser.