Where does “þykia” come from?

þykia (Old Swedish) comes from Old Norse þykkja, from Proto-Germanic þunkijaną — to seem, to appear.

Ancestry of “þykia”, step by step

Step	Language	Word	Meaning
1	Old Norse	þykkja	to be thought to be, seem to be, be esteemed or...
2	Proto-Germanic	þunkijaną	to seem, to appear