Where does “ña” come from?

ña (Spanish) comes from Medieval Latin seniora, from Latin senior, from Latin senex, from Proto-Indo-European sénos — old.

Ancestry of “ña”, step by step

Step	Language	Word	Meaning
1	Medieval Latin	seniora	nominative neuter plural of senior; accusative...
2	Latin	senior	older, elder; rather old; a lord, sir; an abbot
3	Latin	senex	old, aged, elderly; old person, old man, old...
4	Proto-Indo-European	sénos	old

ña — Etymology, Origin & Word History | Etymology Explorer