Onomasiology (from Greek: ὀνομάζω onomāzο 'to name', which in turn is from ὄνομα onoma 'name') is a branch of linguistics concerned with the question "how do you express X?"
It is in fact most commonly understood as a branch of lexicology, the study of words (although some apply the term also to grammar and conversation).
Onomasiology was initiated in the late 19th century, but it received its name only in 1902, when the Austrian linguist Adolf Zauner published his study on the body-part terminology in Romance languages.
Early linguists were basically interested in the etymology of expressions that were clearly-defined, unchangeable, or concrete objects or actions.
The first ones are Sprachatlas des Deutschen Reiches by Georg Wenker and Ferdinand Wrede, published beginning in 1888, the Atlas Linguistique de la France (ALF) by Jules Gilliéron (1902–1920), the Sprach- und Sachatlas Italiens und der Südschweiz (AIS) by Karl Jaberg and Jakob Jud (1928–1940), the Deutscher Sprachatlas (DSA) by Ferdinand Wrede et al. (1927–1956).
The atlases include maps that show the corresponding names for a concept in different regions as they were gathered in interviews with dialect speakers (mostly old rural males) by means of a questionnaire.
In 1931, the German linguist Jost Trier introduced a new method in his book Der deutsche Wortschatz im Sinnbezirk des Verstandes, which is known as the lexical field theory.
After World War II, few studies on onomasiological theory have been carried out (e.g. by Cecil H. Brown, Stanley R. Witkowski, Brent Berlin).