Could someone explain me the differences or nuances between a shiur, d’var Torah, drash (and drashah) as they all seem to refer to ‘a teaching’.
P.s. is there something in their roots which defines the differences between them?
I think the terms are all used to connote a lecture given over by someone, not necessarily distinguishing between them. The only place where we do see specific meanings to those words is in the Talmud.
For common meanings of the words:
Shiur- a lesson given over by a Rav or learned person. In a yeshiva, this is the term to connote the lesson or class given over by the Rav of the class.
D'var Torah- a lesson or Torah-based lecture or conversation about Torah; not necessarily one subject.
Drash- similar to d'var Torah.
I'm really confused about what you're asking for: