A relatively straightforward research question in the study of dead languages is of the form: "We have root XYZ that means A in context P and B in context Q. How can we generalise A and B to arrive at a general meaning for XYZ?" The question can be approached both from a diachronic perspective ("How did meanings A and B derive from older, more general meaning C?") and from a synchronic perspective ("What do A and B have in common, and what aspects characterise both?").
An example of a diachronic approach would be Gluck (1976). The root lḥm in Hebrew and in the Semitic languages. OTSWA (19), pp. 41–43. An example of a synchronic approach would be Kotzé (2016). Comments on the Uses and Meanings of אין in the Masoretic Text of the Hebrew Bible: Revisiting Vriezen. Hebrew Studies (57), pp. 17–38.
How would I call such a study, particularly one with a synchronic approach?