Where does “fichiú” come from?

fichiú (Irish) comes from Old Irish fichetmad, from Old Irish -mad, from Proto-Celtic -metos.

fichiú (Irish): twentieth; twentieth part

Definitions

Step	Language	Word	Meaning
1	Old Irish	fichetmad	—
2	Old Irish	-mad	—
3	Proto-Celtic	-metos	—

fichiú — Etymology, Origin & Word History | Etymology Explorer