More about vox populi
The phrase vox populi comes straight from Latin vōx populī “voice of the people.” Vōx (inflectional stem vōc-) is the source of English vocal and vowel, via Old French vouel, from Latin (littera) vōcālis “sounding (letter).” Populī is the genitive singular of the noun populus, the collective name for the Roman citizen body, excluding women, children, foreigners, and slaves. The phrase vōx populī does not occur in Latin literature and only first appears in a letter that the great Anglo-Saxon scholar Alcuin wrote to Charlemagne in 798, not to pay heed to those who insist that vōx populī vōx Deī “the voice of the people is the voice of God” because the populace is too unstable–a sentiment the Romans would agree with entirely. In later English history (after Alcuin), vōx populī vōx Deī is favorable, a notable example being the title of a Whig tract entitled Vox Populi, Vox Dei: being true Maxims of Government (1710). The abbreviated phrase vox pop “the views of the majority of people, popular opinion” appears in the first half of the 18th century. Nowadays vox pop means “popular opinion as shown by comments made to the media by members of the public.” Vox populi entered English in the mid-16th century.