I have no imagination today, so I let my fingers thumb through the dictionary until they lit upon something promising. Is it my fault that my fingers happen to be pirates at heart?
I don’t think I’ve ever heard this word outside the phrase “scurrilous scalawag.” It could be just that my memory is sharper when aided by alliteration. Who knows? The specific definition is pretty much what your imagination might dream up: “tending to use vulgar language.” Vulgar includes both the sense of being slang and the sense of being taboo (i.e., rude) language. “Scurrilous” also carries the connotation of abusiveness: one who is accused of being such is probably not so called for participating in a friendly round of “your mom” jokes.
Scurrilous is the only form of the word I have ever seen or heard, but apparently there is a secret cult of elite word-users plotting to keep its archaic form “scurrile” alive, because this form is also in the AHCD. If you want to find the etymology of the form that people actually use, you have to pay homage to the form they don’t. Fitting, actually, now that I think about it.
Anyway, “scurrilous” comes barely changed from the Latin (via Old French and French without much damage done) scurrilis, meaning “jeering.” That comes from an older word whose origin is slightly foggy: scurra. The AHCD states that this word meant “buffoon” and probably came from the Etruscans. The Etruscans were the ancient inhabitants of Tuscany whose history is all but gone, save for what got intermingled with their Latin and Sabine rivals. Every time you think of scurrilous scalawags, tip your hat to a civilization long dead and barely remembered.
If you have a dictionary with good etymology entries, take a walk through the “scu-” section and read a few of the entries like a pirate. Here’s a few suggestions to get you started: scurvy, scum, scuttlebutt, scupper, and scuffle.