Where does “sanar” come from?

sanar (Old Spanish) comes from Latin sānō, from Latin -ō, from Proto-Indo-European -ō — Derives nouns from roots.

Ancestry of “sanar”, step by step

Step	Language	Word	Meaning
1	Latin	sānō	to heal, cure
2	Latin	-ō	suffixed to nouns or adjectives. Originally a-stem nouns. Later extended to nouns with other stems. Forms regular first-conjugation verbs
3	Proto-Indo-European	-ō	Derives nouns from roots