Lexicology is the branch of linguistics that concerns the words of a specific language. A word is the smallest meaningful unit of a language that can stand on its own. A word might have one or more small components called morphemes. Lexicology examines every feature of a word – including formation, spelling, origin, usage, and definition.

Lexicology also considers the relationships that exist between words. In linguistics, the lexicon of a language is composed of lexemes, which are abstract units of meaning that correspond to a set of related forms of a word. Lexicology looks at how words can be broken down and identifies common patterns in words.

Lexicology is associated with lexicography, which is the practice of compiling dictionaries.

The term lexicology derives from the Greek word λεξικόν lexicon (neuter of λεξικός lexikos, "of or for words", from λέξις lexis, "speech" or "word") and -λογία -logia, "the study of" (a suffix derived from λόγος logos, amongst others meaning "learning, reasoning, explanation, subject-matter").

Etymology as a science is one of the foci of lexicology. Since lexicology studies the meaning of words and their semantic relations, it often explores the history and development of a word. Etymologists analyze related languages using the comparative method, which is a set of techniques that allow linguists to recover the ancestral phonological, morphological, syntactic, etc., components of modern languages by comparing their cognate material. This means many word roots from different branches of the Indo-European language family can be traced back to single words from the Proto-Indo-European language. The English language, for instance, contains more borrowed words (or loan words) in its vocabulary than native words. Examples include parkour from French, karaoke from Japanese, coconut from Portuguese, mango from Hindi, etc. A lot of music terminology, like piano, solo, and opera, is borrowed from Italian. These words can be further classified according to the linguistic element that is borrowed: phonemes, morphemes, and semantics.

General lexicology is the broad study of words regardless of a language's specific properties. It is concerned with linguistic features that are common among all languages, such as phonemes and morphemes. Special lexicology, on the other hand, looks at what a particular language contributes to its vocabulary, such as grammars. Altogether lexicological studies can be approached two ways:

These complementary perspectives were proposed by Swiss linguist Ferdinand de Saussure. Lexicology can have both comparative and contrastive methodologies. Comparative lexicology searches for similar features that are shared among two or more languages. Contrastive lexicology identifies the linguistic characteristics which distinguish between related and unrelated languages.

The subfield of semantics that pertains especially to lexicological work is called lexical semantics. In brief, lexical semantics contemplates the significance of words and their meanings through several lenses, including synonymy, antonymy, hyponymy, and polysemy, among others. Semantic analysis of lexical material may involve both the contextualization of the word(s) and syntactic ambiguity. Semasiology and onomasiology are relevant linguistic disciplines associated with lexical semantics.