The article discusses the phenomenon of the semantic diffusion, which is realized on different levels of language system, and also in linguistic communication. The author considers the dictionary definitions of the Polish adjective meaning virtual as well as its German and Russian equivalents (virtuell, virtualnyi), and also the results of two psycholinguistic experiments to prove the thesis, that the semantic diffusion is characteristic for the way the adjective functions in communication both on the level of linguistic system (the langue), and on the level of telling (the parole). Interpreting the results of investigations, the author discusses the notions of 'polysemy' and 'ambisemy'.