Infantilism: For Want of a Better Term

I've stated my disagreement with Kathi Stringer's term "True Infantilism" (though not with the concept she uses it to refer to), but I'd like to say something about the term "infantilism" itself.

If you look "infantilism" up in a dictionary, you will see definitions that have to do with arrested development and extreme immaturity. Look at dictionary.com, for example. To paraphrase, the definitions are:

Immature physical or behavioral traits persisting past childhood.

The quality or state of being infantile (i.e. the noun form of the adjective "infantile").

I think those two statements pretty much sum up all the definitions. And neither one of them is a synonym for adult babies, is it? I mean, sure, maybe ABs exhibit infantile behaviors, but you might as well describe the sky by saying it's blue, ignoring everything else you could say about it. The sky contains a variety of wind and cloud patterns that produce different types of weather; it's made up of various gases; the atmosphere consists of different layers, each with its own distinct makeup and phenomena, etc. What's more, there are things that are blue other than the sky.

And there are things that are infantile other than ABs. The term as it has been used until relatively recently is really not very descriptive of ABs at all. ABs can behave in an immature way, but usually this is when they are roleplaying; that is, interacting in a prenegotiated common space. The amount of maturity required to be immature sometimes reaches the paradoxical. Most of the time, ABs act as mature as anybody else -- sometimes more so, depending on whom you compare them with. For example, would you say the language I'm using in this post is immature?

The dictionary definition of the word "infantilism" has to do with immaturity. Then along came somebody (Dr. Wilhelm Stekel, perhaps?) and started using the term for ABs, inventing a new definition for it. But if we're going to go inventing definitions, why not invent an entirely new word, rather than use an old one that has baggage? I think "infantilism" is a failure for describing Whatever It Is That We Do.