The theme of this issue, "the words of science in the Middle Ages" explores a period that has received relatively little attention in languages for special purposes (LSP). In so doing, it opens up a significant avenue of reflection, particularly on the periods, intervals of time and methods considered so far in diachrony, through the lens of LSPs. On this basis, we raise various theoretical and methodological questions, in order to contribute to sketch a portrait of what we would rather call diachronies.