Swedish names usually also has the double "ss" instead of just one s.But my point is that I thought it was Swedish because it ends in 'son', rather than 'sen' (with the ö just disappearing over the years/at some point). However, kristo confirmed that it was indeed originally Danish, ending with 'sen'.
It is never an ö in "son" at the end. It is before if it is in the name.
And son literally means "son" in swedish too. That is where the surname derives from back in the day. If the fathers name was Erik. The sons surname would be Eriksson. Like Eriks son. Hence the double ss. Now they dont make surnames like that no more. The family name just continues.