"Great Calamity" is not among "the definitions that the sources have arrived at." In case you're not aware of it, the Armenian word for "calamity/catastrophe/disaster" is "aghed." According to the abovementioned articles, a number of people have simply written "Medz Yeghern (Great Calamity)"; the author has probed the grounds for such a translation and showed that there are no grounds. (As an analogy, if various people started to write "Shoah (Tragedy)" just from the top of their head, I don't think that the Wikipedia article about the Holocaust would include the unsupported translation "Tragedy" just because any number of people used it.)