Where does “på sin höjd” come from?

på sin höjd (Swedish) comes from Swedish sin, from Old Swedish sīn, from Middle Low German sîn, from Old Saxon *sinn, from Proto-West Germanic sinn, from Proto-Germanic sinnaz, from Proto-Indo-European sentnós, from Proto-Indo-European sent- — to be.

Ancestry of “på sin höjd”, step by step

på sin höjd traces back through 3 separate lines of ancestry.

via Swedish sin

Step	Language	Word	Meaning
1	Swedish	sin	Dryness, the state of having run dry
2	Old Swedish	sīn	Reflexive possessive third person determiner. his (own), her (own), its (own), their (own)
3	Middle Low German	sîn	of his
4	Old Saxon	*sinn	—
5	Proto-West Germanic	sinn	sense, perception; sense, meaning; reason, mental...
6	Proto-Germanic	sinnaz	sense, perception; sense, meaning
7	Proto-Indo-European	sentnós	—
8	Proto-Indo-European	sent-	to head for, to go, to travel; to feel
9	Proto-Indo-European	h₁es-	to be

via Swedish höjd

Step	Language	Word	Meaning
1	Swedish	höjd	raised, increased; a height, an altitude, an...
2	Old Norse	hæð	height
3	Proto-Germanic	hauhiþō	height
4	Proto-Germanic	hauhaz	high
5	Proto-Indo-European	ḱewk-	flare up, glow; white; to glow, burn, lighten

via Swedish på

Step	Language	Word	Meaning
1	Swedish	på	on, on top of; touching from above; on, against,...

Every word from Proto-Indo-European h₁es- →Every word from Proto-Indo-European sent- →Every word from Proto-Indo-European sentnós →