What the fuck is a cranny? If you saw a cranny would you know that it was a cranny and scream out, “look everybody! Look at this fabulous cranny! My! What a cranny it is! I’m going to stick my finger into this here cranny and see if porridge comes out!” This is followed by a ride in an ambulance and a lawsuit.
But this would never happen because nobody uses the word “cranny” anymore. And I’m of the mind that nobody ever did because it’s weird, even for the people of the 15th century when everything was fabulous and gay. And even worse, it’s NEEDY. We never say “cranny” anymore unless it’s paired with “nook”, and even then we make it “every nook and cranny”. It’s not as needy as “remiss” but at least that word doesn’t sound like you picked it off a festering wound on your anus.
A cranny is a crack or a crevice. So I suggest to you all, for the sake of the stupidest children, to change this phrase to “every crack and crevice”. It sounds better, and is more detailed.
Of course, if we wait long enough, and brutally murder everyone who calls their bookstore the “Book Nook”, as well as anyone who likes Ayn Rand because they are assholes, we will all forget the meaning of “nook”, and then the expression “nook and cranny” will go the way of “spic and span”, which is so far removed from its original meaning as to be a fascinating study in the evolution of language, with possible origins in Old Norse, Old English, Middle Dutch, Old High Germanic, Proto-Indo-European, and Latin. Check out its entry in the OED. Walking around with this expression is like carrying an astrolabe in your pocket: totally ridiculous but the history is staggering and you will definitely get laid if you use it correctly.