Finnish word tappo comes from Finnish cotton, Proto-Uralic *tappa- (Trample.)

Detailed word origin of tappo

Dictionary entry	Language	Definition
cotton	Finnish (fin)
*tappa-	Proto-Uralic (urj-pro)	Trample.
thresh	Finnish (fin)
*tappadak	Proto-Finnic (fiu-fin-pro)	To kill, to slay.
tappaa	Finnish (fin)	(transitive, + genitive-accusative) To kill, slay.
tappo	Finnish (fin)	(common language) Voluntary manslaughter under mitigating circumstances.. (legal) A manslaughter.. Killing or kill.

Words with the same origin as tappo