Where does “fastslå” come from?

fastslå (Norwegian Nynorsk) comes from Norwegian Nynorsk slå, from Old Norse slá, from Proto-Germanic slahaną, from Proto-Indo-European slak- — to hit; strike; to hit, strike, throw; to hit,...

fastslå (Norwegian Nynorsk): to establish, ascertain, prove

Definitions

to establish, ascertain, prove

Ancestry of “fastslå”, step by step

fastslå traces back through two separate lines of ancestry.

via Norwegian Nynorsk slå

Step	Language	Word	Meaning
1	Norwegian Nynorsk	slå	to beat, punch, hit
2	Old Norse	slá	to hit, beat, strike; to strike, pluck
3	Proto-Germanic	slahaną	to hit, to strike; to kill
4	Proto-Indo-European	slak-	to hit; strike; to hit, strike, throw; to hit,...

via Norwegian Nynorsk fast

Step	Language	Word	Meaning
1	Norwegian Nynorsk	fast	solid, steady, firm, fixed, permanent, stuck
2	Old Norse	fastr	fast, firm, sticking fast to the spot; close,...
3	Proto-Germanic	fastuz	fixed, firm, secure

Every word from Proto-Indo-European slak- →Every word from Proto-Germanic slahaną →Every word from Old Norse slá →