Where does “artz” come from?

artz (Old French) comes from Latin artes, from Latin ars, from Proto-Italic artis, from Proto-Indo-European h₂értis, from Proto-Indo-European h₂er- — to fit, to fix, to put together.

Ancestry of “artz”, step by step

Step	Language	Word	Meaning
1	Latin	artes	second-person singular present active subjunctive...
2	Latin	ars	art; skill, craft, handicraft, trade, power
3	Proto-Italic	artis	—
4	Proto-Indo-European	h₂értis	fitting
5	Proto-Indo-European	h₂er-	to fit, to fix, to put together

Every word from Proto-Indo-European h₂er- →Every word from Proto-Indo-European h₂értis →Every word from Proto-Italic artis →