vulgo

Vulgo is the ablative of vulgus, "the crowd", frozen into an adverb: "among the crowd", and so "commonly, generally, everywhere, in public". It is the standard tag for the popular name of a thing against its learned one, which is why plants, towns and saints across medieval Latin are all vulgo dictus something or other.

Do not confuse it with the verb it looks like. Vulgo, vulgare, vulgavi, vulgatum is first conjugation and means "to make common, to spread abroad, to publish"; its participle names the Vulgate, Jerome's Bible in the common tongue, and shows up here as vulgatum. Adverb or verb, the sense of the root is the same: what belongs to everybody. English divulge and vulgar come from it, the second having picked up the sneer along the way.