Polly

Polly, which can also be spelled Pollie, is listed by nearly all the "authorities" as being a pet form of Molly. At least Ask Oxford mentions that they don't have a clue why the M in Molly got changed to a P to give Polly. Polly is currently considered a bit of an old-fashioned name--it was in common use in the U.S. until the 1960's when it fell completely out of fashion. The fact that it is associated with parrots (as in "Polly want a cracker?") doesn't help its popularity for human children. So here we have a name with no clear meaning, no clear origin, and associated with an animal to the point of being a cliché, that seems old-fashioned, and also seems like it ought to be a nickname for some other name--can this name ever regain popularity? Probably.