The paper deals with the relations between the synonym pair bodočnost and prihodnost, as well as to a certain extent bodoči and prihodnji, discussed from the point of view of standard language norms and codification, conceptual structure and word use. The analysis is an attempt to answer the question as to what happens to the members of a pair that take on a synonymous relationship because of extra-linguistic factors. For bodočnost, along with bodoči, was borrowed by Slovene in the mid-19th century in the spirit of Slavic mutuality, in spite of the fact that the term prihodnost already existed for the same concept (as well as prihoden/prihodnji). The answer to the question offered by the two mentioned pairs is that the marked member of the pair may either slowly disappear or may try to find its own semantic niche by strengthening and fixing its limited use alongside some other lexeme, forming a pattern ranging from a collocation to a fixed expression. The use of bodočnost points to the first option, whereas in the case of bodoči the selection of fixed phrases supports the second option.