Where does “Ad” come from?

Ad (Latin) comes from Latin illic, from Latin ille, from Latin olle, from Proto-Italic *olnos.

Ancestry of “Ad”, step by step

Step	Language	Word	Meaning
1	Latin	illic	he, she, it, yonder, that, overthere; in that...
2	Latin	ille	that; those; "; demonstrative pronoun "; that...
3	Latin	olle	Archaic form of ille
4	Proto-Italic	*olnos	—

Ad — Etymology, Origin & Word History | Etymology Explorer