Interested in Language
Is there a single word that encapsulates the idiomatic expression "root of a problem"?
I think of words like "nub", "crux" etc that can refer to the core or essence of a problem but not necessarily it's cause and, as Raymott says, you need to add that you are talking about a problem. I can't think of a single-word answer. Maybe that's why it's such a handy phrase.
not a teacher