What is the meaning of Custos?

A warden.

A monastic superior, who, under the general of his order, has the direction of all the religious houses of the same fraternity in a given district, called a custody of the order.

In older forms of musical notation, an indication, at the end of a line of music, of the first note of the next line.

a guard, protector, watchman

a guardian, tutor

a jailer

a keeper, custodian

plural of custo

custodian

Source: wiktionary.org