What is the meaning of Dominus?

master; sir; a title of respect formerly applied to a knight or clergyman, and sometimes to the lord of a manor or an academic master

conditional of domini

master, possessor, ruler, lord, proprietor

owner of a residence; master of his servants and slaves

master of a feast, entertainer, host

master of a play or of public games, employer of players or gladiators

sir (a greeting, in the vocative case)

Source: wiktionary.org