Not only is the word one of the most rhythmic and beautiful I can think of, but it also has a very cool derivation.
Onoma: From the Greek word for name,
-poeia: From the Greek for 'I make'.
So it literally means "Name I make". Which, if you think about it, really doesn't describe what it's meant to be doing at all. The same thing could be applied to someone who compiles baby name books.