advertorial = advertisement + editorial
In print publishing, an advertorial is an advertisement "disguised" as an editorial or other article. There might actually be some informational content in there, but it is all bent toward convincing the reader to buy a particular product.
I suppose I really should stop being surprised by how old some of these portmanteau words are, as if only in the last 30 years or so have people used and enjoyed wordplay. Advertorial has appeared in dictionaries my entire life and has been in use since before my grandfathers were born. It appears, for instance, unabashedly in the May 1914 issue of Kansas City's The Rotarian (page 14) in a subtitle: "A Word to the Women Folk: An Advertorial by Kansas City's Rotary Ad Man."
Outside of the world of marketing, a lay person might not be so gallant to announce that an article is really an advertorial. I, for one, find it difficult to even think, much less say, the word advertorial without rolling my eyes. There's more than enough real stuff to read, I don't need to waste my time getting knee-deep in an advertorial before I realize I should just turn the page.
Other Google Book searches turned up a number of false positives, which is a frustrating find. There were a few actual positives from the 19th century. I didn't look at all of them, but a sample shows that many of these either (a) are in Latin or (b) use advertorial to mean something akin to adversarial.
Had I a decent historical dictionary nearby, I might look to see if this was a common use of this word. But I don't. So I can't.