Where does “foier” come from?

foier (Old French) comes from Vulgar Latin focarium, from Latin focārius, from Latin -ārius, from Proto-Italic *-āzios — Forms relational adjectives to nouns (and rarely numerals).

Ancestry of “foier”, step by step

Step	Language	Word	Meaning
1	Vulgar Latin	focarium	—
2	Latin	focārius	a kitchen-boy
3	Latin	-ārius	er
4	Proto-Italic	*-āzios	Forms relational adjectives to nouns (and rarely numerals)

Every word from Proto-Italic *-āzios →Every word from Latin -ārius →Every word from Latin focārius →