In the decade of the sixties, the main concern of the experts in Basque language was how to unite the speech community. However, after forty years of Standard Basque, the objective is to develop a language that is well adapted to each register. The lexis is the key in the functional development that the adaptation to each register requires, and that is exactly what we shall study in this work. We shall analyse, from the point of view of functional diversity, the methodology of the Standard Basque Dictionary, the purpose of which is to organize the standard Basque lexicon. We reach the conclusion that Standard Basque has taken certain steps to get closer to the functional variability desideratum. However, we have also detected methodological practices that may be an obstacle in this functional development. As a result, we draw up the outline of the methodological changes that would be required to accommodate linguistic norms to the variation at the register level.