Where does “ad pressum” come from?

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

Ancestry of “ad pressum”, step by step

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