Where does “sanctus” come from?

Sanctus derives from Latin sanctus, past participle of Latin sancio, both ultimately from Proto-Indo-European seh₂k-, meaning to sanctify or consecrate.

Ancestry of “sanctus”, step by step

Step	Language	Word	Meaning
1	Latin	sānctus	—
2	Latin	Iacobus	Jacob; James; Saint James
3	Ancient Greek	Ἰάκωβος	—
4	Ancient Greek	Ἰακώβ	—
5	Hebrew	יַעֲקֹב	Jacob
6	Hebrew	עָקֵב	heel of the foot; heel

Every word from Hebrew עָקֵב →

sanctus — Etymology, Origin & Word History | Etymology Explorer