Where does “underlag” come from?

underlag (Norwegian Nynorsk) comes from Norwegian Nynorsk under, from Old Norse undir, from Proto-Germanic under, from Proto-Indo-European h₁entér, from Proto-Indo-European h₁en — in; in, inside.

underlag (Norwegian Nynorsk): a base, basis, foundation; a mat, pad, underlay,...

Definitions

a base, basis, foundation; a mat, pad, underlay,...

Ancestry of “underlag”, step by step

underlag traces back through two separate lines of ancestry.

via Norwegian Nynorsk under

Step	Language	Word	Meaning
1	Norwegian Nynorsk	under	below, beneath, under; during; wonder, marvel,...
2	Old Norse	undir	under, underneath
3	Proto-Germanic	under	among, between; under, beneath; under
4	Proto-Indo-European	h₁entér	between
5	Proto-Indo-European	h₁en	in; in, inside

via Norwegian Nynorsk låg

Step	Language	Word	Meaning
1	Norwegian Nynorsk	låg	low
2	Old Norse	lág	a felled tree; log; lying tree
3	Old Norse	leggja	to lay, place, put; to make, build
4	Proto-Germanic	lagjaną	to lay, to place in a resting position
5	Proto-Indo-European	legʰ-	to lie

Every word from Proto-Indo-European h₁en →Every word from Proto-Indo-European h₁entér →Every word from Proto-Germanic under →