When the word promulgate ("to make widely known") was first brought into the English language in 1526, it was spelled promulgat, and it stayed that way until the e was standardized in the late seventeenth century. It comes from Latin promulgatus, which was the past participle of the verb promulgare, with the same definition. Beyond this, there are two theories. There's definitely the prefix pro-, meaning "forth", but the root could be either an alteration of vulgare, which translates to "to publish", or mulgere, which meant "to milk" (or, more metaphorically, "to bring forth"). Personally, I like the second explanation better because it doesn't make much sense to me that an m would just change to a v unless it was conflated with another word. Mulgere is from Proto-Indo-European melg, "to wipe off".
Hello! I'm Adam Aleksic. This year, I graduated from Harvard University with a degree in Government and Linguistics. There, I co-founded the Harvard Undergraduate Linguistics Society and wrote a thesis on Serbo-Croatian language policy, magna cum laude. In addition to etymology, I also really enjoy philosophy, trivia, vexillology, geography, board games, conlanging, art history, and law.