Grammatical simplicity is the mark of a vernacular. The word ‘vernacular’, formed from the Roman historian Varro’s phrase vernacula verba, ‘unliterary expressions used by slaves or serfs’, has often since been used loosely to mean ‘the native language of a peasantry’; but few of Varro’s slaves can have been native Italians—they may have been Greeks, Bithynians, Africans or Germans—and the language they spoke among themselves was a mixed lingo, sometimes called ‘camp Latin’, which later developed in Italy into modern Italian, in Spain into Spanish, in France into French. Properly speaking, then, a vernacular is a lingo, or language of domestic convenience, compounded of the languages spoken by master and alien slave.

Robert Graves and Alan Hodge, The Reader Over Your Shoulder: A Handbook for Writers of English Prose (1943)