It has been the custom of the editors of the Associated Press Stylebook to announce their annual revisions at the national conference of ACES: The Society for Editing, presumably because those are the people who care what is in the AP Stylebook.
These updates regularly have something to raise the hair on the back of a stickler's neck. This year it is the entry on unique: "The stylebook is changing its guidance on the word 'unique.' The revised entry now says: 'The word can mean one of a kind, unparalleled, having no equal, etc.; or highly unusual, extraordinary, rare, etc. If used in the sense of one of a kind, don’t use modifiers such as very, rather, etc.' "
One can still hear keening over the abandonment of the unfounded over/more than distinction or the heaving over the side of the "split verb" rule, which held against all evidence than one cannot insert an adverb between an auxiliary and the main verb (and which I take some pride in having campaigned against for years).
The editors of the AP Stylebook are not wild-eyed Jacobins; they endorse changes in usage only after those changes have been in wide use for years.
Regarding unique: Jeremy Butterfield in Fowler 4 comments on the sense of "particularly remarkable, special, or unusual," remarking, "All modern monolingual dictionaries recognize this meaning, usually with a warning."
American Heritage in 2011 upheld the absolute sense of the word but conceded, "In fact, the nontraditional modification of unique may be found in the work of many reputable writers and has certainly been put to effective use."
Merriam-Webster's Dictionary of English Usage (1994) explains, "Words that are in widespread use have a natural tendency to take on extended meanings. In the case of unique, it was natural that a word used to describe something that was unlike anything else should also come to be used more broadly to describe something that was, simply, unusual or rare," the latter use having been common for more than a century.
Bryan Garner clucks that the looser usage is in his Stage 3 of language change: "Widespread, but ..."
Unique we lifted from the French, who had it from the Latin unicus, "one." I suspect that insistence on the absolute meaning rises in part from the etymological fallacy, the belief that the meaning of a word must be restricted to its original sense. You may know people who insist that decimate must refer for the destruction of a tenth rather than substantial damage. I used to teach my students at Loyola that dilemma had to mean two unsatisfactory choices, like Odysseus having to decide between Scylla and Charybdis, because the Greek root di- means "two." I have no way to get back to them now to say that it can simply mean "a difficult situation."
English is on the move, and has been since we and the French destroyed Anglo-Saxon. And though it will likely lead to by expulsion from the Stickler Sodality, I recommend judgement instead of rigid adherence to rules of dodgy provenance. Figure out what will make sense to the reader.
