In modern English, you can usually add “-ly” to a word to use it in a slightly different way. That is, if there’s something you do most of the time — it’s your “usual” practice — then you could also say you do that thing “usually.”
This goes back to Old English, except that where we use “-ly,” Old English used “-lic,” or even “-like.” There are a few words where we still use “-like,” such as “the monkey had a humanlike reaction.” And “like” is the source of the whole thing, really. Your “usual” practice is “usual like” — it’s similar to what’s usual. And sure enough, if you go even further back than Old English, into ancient Germanic words, you find “like” attached to words to make new words.
That was the way Old English worked; you could make up new words by combining existing words. That’s not exactly how modern English works — except of course, that sometimes it is. See what I did there? “Some” and “times”? But back to the “-ly” suffix. Typically, (just did it again!) an English word that ends in “-ly” is used to describe something. Except, of course, that occasionally it isn’t.
Take, for example, “contumely.” It wasn’t formed by adding “-ly” to “contume.” For that matter, “contume” isn’t a word at all. “Contumely” means insulting language, and it’s been around for a long time too; Chaucer used it in “The Parson’s Tale:” “The sinne of contumelie or strif and cheste.”
The reason “contumely” sounds weird to English speakers (well, once they know what it means, anyway), is that it’s not a Germanic word, and the resemblance to other “-ly” words is just a coincidence. It comes from Old French: “contumelie,” which meant the same thing as in English.
You might, of course, need to describe something as being “like” contumely. And you know how English words, over time, often get abbreviated and shortened. Well they often do — except, of course, when they don’t. If you want to describe somebody’s speech as being like contumely, you can say it’s delivered “contumeliously.” That’s right, back in the 1500s they went and added “-ly” to a word that already ended in “ly.” Now that’s being resourceful-like.
