Where does “fejtsünk” come from?

fejtsünk (Hungarian) comes from Hungarian fejt, from Hungarian -t, from Proto-Uralic -tt.

Ancestry of “fejtsünk”, step by step

Step	Language	Word	Meaning
1	Hungarian	fejt	to unstitch, untack; to husk, shell, hull, pod;...
2	Hungarian	-t	Used to form the accusative case; -ed, -t. Used...
3	Proto-Uralic	-tt	—