Where does “yako” come from?

yako (Ido) comes from English yak, from Korean 약, from Japanese 役, from Middle Chinese 役.

yako (Ido): yak

Definitions

Step	Language	Word	Meaning
1	English	yak	An ox-like mammal native to the Himalayas,...
2	Korean	약	drug; medicine; approximately; about; an ancient...
3	Japanese	役	role, service, use; hand, scoring combination;...
4	Middle Chinese	役	—

yako — Etymology, Origin & Word History | Etymology Explorer