ploughman, or oxman
Bovarius, translated as ploughman in the Phillimore edition, is sometimes rendered as oxman, its literal translation.
Ploughmen were almost entirely confined to the four counties of Cheshire, Hereford, Shropshire and Worcester, all in circuit 5, just a single ploughman being recorded elsewhere in Domesday. This is certainly an eccentricity of data collection or compilation by the commissioners since considerable numbers of ploughmen are recorded in other counties in twelfth-century sources.
As their name implies, ploughmen drove the plough team, that is the lord's plough team, a function also performed by slaves. On this basis, it has been plausibly suggested that ploughmen may be slaves freed by their lord and endowed with small plots of land - half-virgates are recorded - on the lord's demesne to support themselves in return for continuing their ploughing services. The Domesday record tends to support this thesis. Not only did slaves often perform the same function as ploughmen but they are sometimes found doing so alongside the ploughmen on the demesne. Ploughmen are also occasionally called 'free ploughmen', as though their status was in doubt.
If there were a tendency to convert slaves into 'free ploughmen', this would certainly help to explain the otherwise astonishingly rapid decline of slavery by the early twelfth century.
For more detail, see M.M. Postan, The famulus: the estate labourer in the XIIth and XIIIth centuries (1954); H.C. Darby, Domesday England (1977); and David Pelteret, Slavery in early medieval England from the reign of Alfred until the twelfth century (1995).