vulgus

Vulgus, vulgi, second declension and neuter, which makes it one of a tiny handful of neuters in -us. The practical consequence is the accusative: vulgus, not vulgum, though a masculine vulgum does surface in verse where the metre needs it. Also spelt volgus in older texts.

The tone is contemptuous far more often than not. Horace's profanum vulgus is the uninitiated mass to be kept at arm's length, and writers reach for populus when they want dignity. The ablative vulgo hardened into an adverb meaning "commonly, everywhere, in public", which is what stands behind vulgate, the Vulgate itself, and the English vulgar - a word that has carried the sneer over completely intact.