The branch of the study of language concerned with the meaning of words and word equivalents is called semasiology. The name comes from the Greek word semasia meaning signification

The branch of the study of language concerned with the meaning of words and word equivalents is called semasiology. The name comes from the Greek word semasia meaning signification. As semasiology deals not with every kind of meaning but with the lexical meaning only, it may be regarded as a branch of Lexicology.
This does not mean that a semasiologist need not pay attention to the grammatical meaning. On the contrary, the grammatical meaning must be taken into consideration in so far as it bears a specific influence upon the lexical meaning.
If treated diachronically, semasiology studies the change in meaning which words undergo. Descriptive synchronic approach demands a study not of individual words but of semantic structures typical of the language studied and of its general semantic system.
Sometimes the words semasiology and semantics are used indiscriminately. They are really synonyms but the word semasiology has one meaning, the word semantics has several meanings.
Academic or pure semantics is a branch of mathematical logic originated by Carnap. Its aim is to build an abstract theory of relationships between signs and their referents. It is a part of semiotics – the study of signs and languages in general, including all sorts of codes (traffic signals, military signals). Unlike linguistic semantics which deals with real languages, pure semantics has as its subject formalised language.
Semasiology is one of the youngest branches of linguistics, although the objects of its study have attracted the attention of philosophers and grammarians since the times of antiquity. A thousand years before our era Chinese scholars were interested in semantic change. We find the problems of word and notion relationship discussed in the works of Plato and Aristotle and the famous grammarian Panini.
For a very long period of time the study of meaning formed part of philosophy, logic, psychology, literary criticism and history of the language.
Semasiology came into its own in the 1830’s when a German scholar Karl Reisig, lecturing in classical philology, suggested that the studies of meaning should be regarded as an independent branch of knowledge. Reisig’s lectures were published by his pupil F. Heerdegen in 1839 some years after Reisig’s death. At that time, however, they produced but little stir. It was Michel Breal, a Frenchman, who played a decisive part in the creation and development of the new science. His book “Essai de semantique” (Paris, 1897) became widely known and was followed by a considerable number of investigations and monographs on meaning not only in France, but in other countries as well.
The treatment of meaning throughout the 19^th century and in the first decade of the 20^th was purely diachronistic. Attention was concentrated upon the process of semantic change and the part semantic principles should play in etymology. Semasiology was even defined at that time as a science dealing with the changes in word meaning, their causes and classification. The approach was “atomistic”, i.e. semantic changes were traced and described for isolated words without taking into account the interrelation of structures existing within each language. Consequently, it was impossible for this approach to formulate any general tendencies peculiar to the English language.
As to the English vocabulary, the accent in its semantic study, primarily laid upon philosophy, was in the 19^th century shifted to lexicography. The Golden age of English Lexicography began in the middle of the 19^th century, when the tremendous work on the many volumes of the Oxford Dictionary of the English Language on Historical Principles was carried out. The English scholars R.C. Trench, J. Murray, W. Skeat constantly reaffirmed the primary importance of the historical principle, and at the same time elaborated the contextual principle. They were firmly convinced that the complete meaning of a word is always contextual, and no study of meaning apart from a complete context can be taken seriously.
Since that time indications of semantic change were found by comparing the contexts of words in older written records and in contemporary usage, and also by studying different meanings of cognate words in related languages.
In the 20^th century the progress of semasiology was uneven. The 1930’s were said to be the most crucial time in its whole history. After the work of F. de Saussure the structural orientation came to the forefront of semasiology when Jost Trier, a German philologist, offered his theory of semantic fields, treating semantic phenomena historically and within a definite language system at a definite period of its development.
In the list of current ideas stress is being laid upon synchronic analysis in which present-day linguists make successful efforts to profit by structuralist procedures combined with mathematical statistics and symbolic logic.