Lexical semantics is a subfield of linguistic semantics. It is the study of how and what the words of a language denote (Pustejovsky, 1995). Words may either be taken to denote things in the world or concepts, depending on the particular approach to lexical semantics.
The units of meaning in lexical semantics are lexical units, which a speaker can continually add to throughout their life, learning new words and their meanings. By contrast, one can only easily learn the grammatical rules of one's native language during a critical period when one is young.
Lexical semantics covers theories of the classification and decomposition of word meaning, the differences and similarities in lexical semantic structure between different languages, and the relationship of word meaning to sentence meaning and syntax .
One question that lexical semantics explores is whether the meaning of a lexical unit is established by looking at its neighbourhood in the semantic net (by looking at the other words it occurs with in natural sentences), or if the meaning is already locally contained in the lexical unit. Another topic that is explored is the mapping of words to concepts. As tools, lexical relations (defined as patterns of association that exist between lexical items in a language) like synonymy, antonymy (opposites), hyponymy and hypernymy - and to a certain degree homonymy as well - are used in this field.