Where does “fostær” come from?

fostær (Old Danish) comes from Old Norse fóstr, from Proto-Germanic fōstrą, from Proto-Indo-European peh₂- — to protect; to shepherd.

Ancestry of “fostær”, step by step

Step	Language	Word	Meaning
1	Old Norse	fóstr	rear, raise; nurturing, education, alimony, child...
2	Proto-Germanic	fōstrą	fostering
3	Proto-Indo-European	peh₂-	to protect; to shepherd

fostær — Etymology, Origin & Word History | Etymology Explorer