vulgar [LME] Latin vulgus ‘the common people’ is the source of vulgar. The original senses, from the late Middle Ages, were ‘used in ordinary calculations’, which survives in vulgar fraction [L17th], and ‘in ordinary use, used by the people’, which survives in vulgar tongue [L16th]. The sense ‘coarse, uncultured’ dates from the mid 17th century. Divulge [LME] is from the same root, from Latin divulgare ‘to spread among the people’, hence to make generally known.