An interesting question! No idea. But I checked. The "hol" part comes from an ancient, Ural-originated word, meaning "morning".
That is interesting, how the Spanish "mañana" is also used for "tomorrow" and "morning". And, btw, "tomorrow" and "morning" also seem to be sharing some distant ancestor.
You might also ask where "tegnap" (yesterday) comes from. No idea. But I checked. It also comes from the Ural-era. "Te-g(e)-nap", "te" being "this", etc., it is a bit blurry and not that important.
The similarity of "tomorrow" and "morning" is also very uncanny in German: "morgen" and "Morgen". :)
It is, but its not realy thought of as a compound word. Simmilar to tomorrow in english.
the dual usage of vagy (and mi) is rather inconvenient. Today you are tomorrow? was my first thought... Here it is quite clear that that is nonsense, but i guess this might cause me some trouble understanding something in the future.