Where does “Celtiad” come from?

Celtiad (Welsh) comes from Welsh Celt, from Latin Celta, from Latin Celtae, from Ancient Greek Κελτοί, from Proto-Celtic kel-to, from Proto-Indo-European ḱelh₂- — to pierce, strike; to stick; prick; stab.

Ancestry of “Celtiad”, step by step

Step	Language	Word	Meaning
1	Welsh	Celt	Celt member of ancient people
2	Latin	Celta	a Celt
3	Latin	Celtae	the Celts
4	Ancient Greek	Κελτοί	the Celts
5	Proto-Celtic	kel-to	—
6	Proto-Indo-European	ḱelh₂-	to pierce, strike; to stick; prick; stab

Every word from Proto-Indo-European ḱelh₂- →Every word from Proto-Celtic kel-to →Every word from Ancient Greek Κελτοί →