Augustine of Hippo gives his two drachma on the etymology of the word servus, which means “slave” in Latin.
The origin of the Latin word for slave is supposed to be found in the circumstances that those who by the law of war were liable to be killed were sometimes preserved by their victors, and were hence called servants. (Servus, “a slave,” from servare, “to preserve.”)
One who is saved from execution becomes a servant. This fits in very well with Paul’s words about Christians being slaves to Christ. I wonder if Augustine had that connection in mind. Unfortunately, it doesn’t work with the corresponding Greek word, doulos, which comes from a verb meaning “to bind.” The Latin servant is the saved one, the Greek servant is the bound one.