Lexicology as a branch of linguistics

Lexicology
(from Gr lexis “word” and logos “learning”) is a part of linguistics dealing with the vocabulary of a language and the properties of words as the main units of the language. It also studies all kinds of semantic grouping and semantic relations: synonymy, antonymy, hyponymy, semantic fields, etc.

The subject-matter of lexicology
word, its morphemic structure, history and meaning.

Branches of lexicology
General lexicology
Special lexicology
Contrastive lexicology
Historical lexicology (etymology)
Semasiology
Onomasiology
Descriptive lexicology

Approaches to the language within the framework of lexicology
The synchronic approach is concerned with the vocabulary of a language as it exists at a certain time (e.g., a course in Modern English Lexicology);
The diachronic approach deals with the changes and the development of the vocabulary in the course of time.

general linguistics,
the history of the language,
phonetics,
stylistics, and grammar.
Lexicology interrelations with other sciences

First, the word is a unit of speech which serves the purposes of human communication. Thus, the word can be defined as a unit of communication.
Secondly, the word can be perceived as the total of the sounds which comprise it.
Third, the word, viewed structurally, possesses several characteristics.
Word nature

The external structure of the word - its morphological structure. For example, in the word post-impressionists the following morphemes can be distinguished: the prefixes post-, im-, the root –press-, the noun-forming suffixes -ion, -ist, and the grammatical suffix of plurality -s.
The internal structure of the word - the word's semantic structure (its meaning). This is the word's main aspect.
Word Structures