vulgar (adj.) late 14c., “common, ordinary,” from Latin vulgaris, volgaris “of or pertaining to the common people, common, vulgar, low, mean,” from vulgus, volgus “the common people, multitude, crowd, throng,” for which de Vaan offers no further etymology. The meaning “coarse, low, ill-bred” is recorded by 1640s, probably from earlier use (with reference to people) in the meaning “belonging to the …
John N. White 