The semantic derivation is an active process of words’ formation. This phenomenon represents the transfer of the noun from one object to another. This process generates the formation of common nouns (appellatives) and proper nouns (toponyms, anthroponyms etc.). This article focuses on the formation of onymic units, especially of place names, through the semantic derivation. The toponymisation is done by the words’ functional-semantic extending in the denomination (polysemy) process, by the name transferring because of a comparison (metaphor) by replacing the name in situations of contiguity (metonymy), by substituting the name on the strength of real or imaginary analogies (symbolisation). A special phenomenon is the passing of proper names into the category of common names (appellativisation); this process is also studied in the article.