Where does “galtza” come from?

galtza (Basque) comes from Late Latin calcea, from Latin calceus, from Latin calx, from Ancient Greek χάλιξ — small stone, pebble; gravel, rubble.

Ancestry of “galtza”, step by step

Step	Language	Word	Meaning
1	Late Latin	calcea	—
2	Latin	calceus	shoe
3	Latin	calx	limestone; chalk; the finish line
4	Ancient Greek	χάλιξ	small stone, pebble; gravel, rubble