Where does “abierto” come from?

abierto (Old Spanish) comes from Latin apertus, from Latin aperiō, from Proto-Indo-European h₂epó — off, away.

Ancestry of “abierto”, step by step

Step	Language	Word	Meaning
1	Latin	apertus	opened, open, free; public; having been opened;...
2	Latin	aperiō	to uncover, make or lay bare, reveal, clear
3	Proto-Indo-European	h₂epó	off, away