Where does “tríocha” come from?

tríocha (Irish) comes from Middle Irish trícha, from Old Irish trícho, from Proto-Celtic *trīkonts.

tríocha (Irish): thirty

Definitions

Step	Language	Word	Meaning
1	Middle Irish	trícha	—
2	Old Irish	trícho	thirty
3	Proto-Celtic	*trīkonts	—

tríocha — Etymology, Origin & Word History | Etymology Explorer