Georgina hands the baby to Auxillia, her aptronymic nanny.
This sentence, from the otherwise spectacular book When A Corocodile Eats the Sun, is a perfect example of how not to write.
First of all, let's dispense with an obvious task and define the word aptronymic, a showoff word that perhaps one in ten thousand people might know. An aptronym is simply a name that is perfectly apt. And thus the joke here is that Auxillia truly is an apt name for a nanny.
It's witty, yes, but the pretentiousness kills the humor. There is absolutely no reason to send 99.99% of your readers running to their dictionaries when you could use a perfectly understandable word in its place. Try "aptly-named" instead, and 100% of your readers will both understand it and get the joke.
Don't be a showoff. Write to your readers, not to the vocabulary gods.