To secularize something is to take religious control or religious colour off it. A government might secularize the schools, so that one church no longer owns them or sets their rules. A building that was a church might be secularized and used as a hall or a museum. You can secularize a law or a holiday so that it no longer belongs to one faith. It is a formal verb, used by writers, courts, and historians more than by friends chatting. The idea is ‘make it belong to ordinary public life,’ not ‘make people stop believing.’ Though actually, the same spelling with -ise (secularise) is common in British English; the meaning does not change.

使世俗化