Lexical semantics is the study of the meanings of words. As well as the simple meaning of a lexical unit, lexical semantics studies how a word represents the meaning it conveys. In this sense, it studies the word’s existence as a whole. While grammar is picked up as a child, an individual can expand his or her lexicography throughout his or her life.
A lexical unit is a single word or run of words that creates the most basic level of a language’s lexicon or vocabulary. The study of these units is called lexicology. Examination of lexical units moves beyond the meanings, as seen in lexical semantics, and moves on to structures and sub-structures of words. The study of the origin of lexical units and vocabulary in general is called etymology. These studies are distinct from lexical semantics, which concentrates on meanings alone.
Base lexical units do not take into account more complex word compounds. Two lexical units, sometimes more, can combine to form a compound with a new meaning. Sometimes this meaning is linked to both words, but other times it is metaphor. Each compound is considered one unit in lexical semantics because it provides a different meaning.
A run of lexical units that combines to provide an overall meaning is called a lexical chain. Lexical chains ignore the grammar functions of a sentence and, in fact, remove them to leave only the words that provide meaning. By removing the function words, or vocabulary, the information words can be strung together in a chain.
Classification is the process by which words are separated from one another. These classifications are usually by meaning or function. Once classified into broad categories, words are then sub-divided within the category. Of course, there are many words with multiple meanings, known as polysemy, which may fall into more than one category.
Words may also decompose. Word decomposition is the phenomenon where words lose their original meaning over time. This is a separate element of lexical semantics compared to classification, because the old word meanings have now become relics or fossils. Rather than morphing into a new meaning, true word decomposition occurs when the word has lost its recognizable meaning, such as in the case of Old English words such as “ascylfan,” meaning to destroy. Others are half-decomposed like an atomic half-life so people understand the meaning of “disheveled” and “ruthless,” but do not know the meaning of “sheveled” and “ruth.”
The study of lexical semantics also broadens out from the study of a single language. It is also an element of comparative and contrastive linguistics. In this sense, lexical semantics compares and contrasts the meanings of identical words between languages. There are multiple instances of words crossing languages, but having the meanings altered, and there are also instances of words forming from different origins that look on the surface to be the same, but have totally different meanings.