The story goes that Warren Harding, the 29th US President, had, during his pre-election campaign, sent his mistress Carrie Fulton a letter with a long list of code words, which he said they would need to start using in their letters from there on. The list included words like 'cloudy', which meant 'message not clear'; 'repair' which meant 'I will meet you in New York'; and (my favourite) 'grateful', which stood for 'all my love to the last precious drop'.
As you can see, especially from the last word, the code was not just utilitarian, it had been carefully constructed to deliver all the romance of a beautifully crafted love letter in plain view and yet hidden from prying eyes.