The article determines the language units' transition from one lexico-grammatical class to another and vice-versa as a «units' migration» giving also a definition of the term «migratory process» in the system of the Portuguese language. These words are unified to «migratory groups», possessing morphological categories common for the lexico-grammatical classes between which they are located or «migrate», according to the article.

lexico-grammatical class, functional-semantic area, migratory group of the words, functional homonymy, polyfunctionality, polysemanticism, peripheral indicators, meaning of quantitativity, meaning of adverbial relativity