The Latin word sclavus, the common source of the words esclave, esclavo, escravo, schiavo, Sklave, and slave, did not take root during that initial period [pre-Middle Ages] when slavery was common to the whole of Europe… . It was only when slaves were recruited from entirely new sources that other terms appeared to indicate the nonfree, and among these were sclavus, derived from the ethnic name of the Slav people and popularized.

Cedric J. Robinson, Black Marxism_ The Making o…, loc. 1522