If you google "хоть шаром покати" (хоть шаро́м покати́) you will find quite a few examples – please could you explain this idiom to me? Apparently it means ‘completely empty’, at least, that is what my Oxford Russian dictionary says, but what do the individual words mean and how does the grammar work?
In particular, what does хоть mean here? Does шаро́м mean ‘like a шар (ball)’?
Best wishes, and many thanks,
You are right that the phrase means 'completely empty'. Now, since you are interested in the grammar, I hope you know all about cases of nouns in Russian.
1. The phrase is a little archaic. People don't put words like this anymore. Unless they want to use the archaic manner.
2. Хоть marks the provisional suggestion like the English 'even if' or 'though'. It's a colloquial form of "хотя", while the full standard form would be "хотя бы".
3. Покати is the singular imperative of покатить which is a bit archaic too.
4. Шаром is the instrumental case of шар / ball. Using the instrumental here is, again, somewhat archaic.
5. The literal meaning points to a storage place which is so empty that a ball can roll freely down the floor, or a shelf, etc.
Hope the above helps,