Where does “Proto-Celtic” come from?

Proto-Celtic (English) comes from English Celtic, from French celtique, from Latin Celticus, 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.

Proto-Celtic (English): The putative ancestor of all the known Celtic languages

Definitions

The putative ancestor of all the known Celtic languages

Ancestry of “Proto-Celtic”, step by step

Step	Language	Word	Meaning
1	English	Celtic	Of the Celts; Of the style of the Celts
2	French	celtique	Celtic
3	Latin	Celticus	Celtic; the Celtic language
4	Latin	Celta	a Celt
5	Latin	Celtae	the Celts
6	Ancient Greek	Κελτοί	the Celts
7	Proto-Celtic	kel-to	—
8	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 →