Other forms: sanctified, sanctifying, sanctifies
To sanctify something is to make it holy. A church is sanctified, a marriage is sanctified, ground is sanctified before anyone is buried in it.
The word is religious first and it stays close to that root: a priest sanctifies, and the noun for the act is sanctification. The second sense is the one you meet in argument, and it is usually a complaint — to sanctify a practice is to treat it as beyond question simply because it has always been done, as in tradition sanctified the arrangement. The related family is large and useful: sacred, sanctuary and saint all come from the same idea of setting something apart.
Sanctify is making holy. Latin sānctus, holy, joins faciō, to make, and the English spelling was later pulled back towards the Latin from the Anglo-Norman seintefier it arrived as.
Proto-Indo-European
*dʰeh₁-
Latin
sānctificō
Old French
saintefier
Anglo-Norman
seintefier
English, today
sanctify
Built from
From Anglo-Norman seintefier, from Old French saintefier, from Latin sānctificō, from Latin sānctus (“holy”) + faciō (“do, make”). Form altered to conform with Latin.
Etymology from Wiktionary, CC BY-SA