Sure Thing

Here's a sentence from The New Yorker's David Denby's review of "The Good German":

The last of those incomparable movies was shot in Berlin, with its cracked and carious buildings, but where Soderbergh is in search of a look, controlling every nuance of a reconstructed style, Rossellini is, more simply, in search of the truth.

The sentence is fine: I'm just in love with the word "carious", and I wanted you to see the context.

I was very briefly puzzled by the word--i'd never seen it before--and then I divined that it must be the adjectival form of the word "caries", meaning "decay", which, in the context of the sentence, makes perfect sense. And in fact, that's exactly what "carious" means. Score one for common sense!

And then I realized that it sounds so much like "precarious", with the prefix "pre-", "before", affixed to it, that "precarious" must mean "teetering on the edge of decay and collapse". It makes perfect sense!

And it's completely wrong!

"Precarious" actually comes from Latin "precari", "to entreat". This, of course, makes no sense whatever, until you follow the thread of its evolution. "Precari" is the ancestor of our "pray", which is to say "entreat". Just praying for something doesn't mean you're going to get it--so capricious, gods--and so the Latin word "precarius" means "uncertain", which is what led to our "precarious", "uncertain, insecure, unstable".