"We must away ere break of day": What is this grammar? Is it alive?
Solution 1:
In this example, away means go away. The verb go is suppressed. It is an archaism, the sort of thing that Tolkien was fond of. It is rare in modern texts, but has been around for hundreds of years.
Here are some examples from the New English Dictionary:
1375 Otherwais mych thai noch avay.
1393 Whither awaie with my hens, foxe?
1594 I will away to Barnet presently.
1623 We must away euery man to his lodging.
1872 Meantime we must away.