I’ve never seen this word before. My spell checkers all reject it. When I look it up in my dictionary app, it isn’t there; not only that, but the app tries to correct it to the word with which I’m much more familiar: vagary, for which it is apparently an "eggcorn."
I love the neologisms that language lovers come up with to categorize the creative mistakes people make. My personal favorite for a while has been mondegreen, but eggcorn may take its place.
The eggcorn, Wikipedia tells us, "is an idiosyncratic substitution of a word or phrase for a word or words that sound similar or identical in the speaker’s dialect." Unlike a malapropism, however, the eggcorn
introduces a meaning that is different from the original, but plausible in the same context, such as “old-timers’ disease” for “Alzheimer’s disease."
The term comes from the substitution of "egg corn" for the word acorn. (You can find a huge list of eggcorns here.) But back to yesterday’s word of the day.
Vagaries (I always encounter the word in the plural) are unpredictable changes, as in the vagaries of fate or the vagaries of the economy. They are not vague. The vagaries of the stock market are ups and downs, profits and losses that we can’t see coming. But while we may not know what those changes will be, we have a very clear understanding of what the possibilities are.
I have often seen writers misuse the word, either to mean "vaguenesses" (or vagueries, if Wiktionary is to be trusted) or in a way that is ambiguous enough that I can’t tell if they intend the word to carry its unpredictable-change meaning.
When King Croesus of Lydia asked the oracle at Delphi whether or not he should confront Cyrus the Great on the battlefield, he was trying to avoid the vagaries (unpredictability) of fate. But what he got back from Delphi were the vagueries (equivocal predictions) of the oracle: if the Lydian king made war on the Persian king, he would destroy a great empire. Croesus took the ambiguous answer one way, and the battle went the other way, destroying Croesus’s own empire. Tricky oracle: either way, she got to keep her job.
So if a writer makes reference to "the vagaries of oracular prophecy," you know he or she probably means vagueries, not vagaries, but it’s probably best to do more than just correct the spelling. A better word choice is needed. And if instead the text you’re editing says, for example, "the vagueries of fate," well, that may or may not be spelled correctly, depending on what the writer means, but it’s probably still best to avoid the vaguery of the word vagueries. Go for something more precise.