Yes, many words that started out as two words separated by a hyphen merge to become one as language evolves. Notebook is a good example of this; a more recent example would be email.

In German it happens even more quickly.

I thought you only used hyphens in German in exceptional circumstances like proper names in compounds? Karl-Marx-Allee etc.

Well, what I meant was that concepts made up of several words almost immediately become one word in German (without hyphens).