Where does “jenero” come from?

jenero (Old Spanish) comes from Arabic يناير, from Latin iānuārius, from Latin -ārius, from Proto-Italic *-āzios — Forms relational adjectives to nouns (and rarely numerals).

Ancestry of “jenero”, step by step

Step	Language	Word	Meaning
1	Arabic	يناير	January first month of the Gregorian calendar
2	Latin	iānuārius	of January
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 iānuārius →