The English word “master” comes from the Latin “magister,” which is freighted with thousands of years of meanings and history. The meaning of slaveowner was not one of those meanings until probably the seventeenth or eighteenth century. In Latin, “magister,” never meant the master of slaves (a “herus” most properly, or a “dominus,” an owner of anything with legal title to that thing). Instead, the “magister” was a leader of a group: the “magister equitum” was a cavalry commander, and a “ludi magister” a schoolmaster or classroom teacher. It is from the latter that we have “master” in the sense of an MA (magister artium) degree, which, like the PhD, was originally a teaching license. The use of the English “master” to refer to slavery is comparatively recent and might well not predate the eighteenth century.