The term consists of Greek morphemes:
lexis logos
(word, phrase) (learning).
Lexicology studies words and phrases, i.e. vocabulary of a language.
Vocabulary consists of:
words - basic units of a given language which are the result of the association of a given meaning with a given group of sounds;
set-expressions = phraseological units - traditional stable phrases like «to rain cats and dogs», «as hungry as a wolf».
Lexicology investigates the problems of words, word-structure, word-formation in the language, the meaning of the words, the main principles of classification of the words, the laws governing the enlarging (replenishment) of the vocabulary.
Kinds of lexicology:
general - deals with the general study of words irrespective of the specific features of any particular language;
special - studies the characteristic features of the vocabulary of a given language;
historical - studies the origin, change and development of the words;
descriptive - studies the vocabulary of a given language at a given stage of its development.