Where does “peaaju” come from?

peaaju (Estonian) comes from Estonian pea, from Proto-Finnic pää, from Proto-Uralic päŋe — head.

peaaju (Estonian): brain

Definitions

Step	Language	Word	Meaning
1	Estonian	pea	head; almost; soon, immediately, quickly
2	Proto-Finnic	pää	head
3	Proto-Uralic	päŋe	head

peaaju — Etymology, Origin & Word History | Etymology Explorer