Where does “mellomnorsk” come from?

mellomnorsk (Norwegian Nynorsk) comes from Norwegian Nynorsk norsk, from Middle Norwegian nornskr, from Old Norse norrǿnn, from Old Norse norðrǿnn, from Proto-Germanic nurþrōnijaz, from Proto-Germanic nurþraz, from Proto-Indo-European *nér — below the surface, below.

mellomnorsk (Norwegian Nynorsk): Middle Norwegian

Definitions

Middle Norwegian

Ancestry of “mellomnorsk”, step by step

mellomnorsk traces back through two separate lines of ancestry.

via Norwegian Nynorsk norsk

Step	Language	Word	Meaning
1	Norwegian Nynorsk	norsk	Norwegian
2	Middle Norwegian	nornskr	Norwegian
3	Old Norse	norrǿnn	northern
4	Old Norse	norðrǿnn	northern
5	Proto-Germanic	nurþrōnijaz	northern
6	Proto-Germanic	nurþraz	north, northern
7	Proto-Indo-European	*nér	below the surface, below

via Norwegian Nynorsk mellom

Step	Language	Word	Meaning
1	Norwegian Nynorsk	mellom	between; among
2	Old Norse	í millum	—

Every word from Proto-Indo-European *nér →Every word from Proto-Germanic nurþraz →Every word from Proto-Germanic nurþrōnijaz →