Can something be initializable?

I think the question --- other than the pedantic one about the word, which I'll mention below --- is what the behavior you intend to identify by this "Initializable" tag might be.

It's not an uncommon style to write a private method init() in, eg, Java to do complicated initialization; since that code may be needed in several places (what with copy constructors, clone operations and so on) it's just good form. Its less common, but a valid thing to so, to have a "Forward" class that is constructed, but that is waiting for some asynchronous operation in order to be fully initialized (eg, the Asynchronous Completion Token pattern). So it's not necessarily so that this should be just in the ctor, but I'm curious what the actual behavior you want would be.

On the word, English is a somewhat agglutinating language, like German: there are grammatical rules that construct works from base words and ther syllables in patterns. one of those is the one here, "Initial" -> "initialize" => "initializable". Any native speaker will recognize "initializable" as something that has the property of being able to be initialized. So it is a value word, but one they don't have in the dictionary for the same reason that don't have separate entries for the plurals.

How about -

interface ICanBeInitialized

or...(and I had a little xmas drinky...so sorry)

interface ICanHazInitialization

Technical people create new words all the time. (see example below) But this isn't a case of creating a new word. This is a case of a "derivation". You have take a perfectly good word ("initialize") and added a perflecty good derivative suffix to it ("able"). The resulting word initializable is a derivative word.

In short, if something can be initialized, it is initializeable. Just like it can be runable, or stopable.

Now, I don't think it will be long before a grammar Nazi points out the error of my ways here. But English is rich and expressive language. A word doesn't have to be listed on "dictionary.com" for it to be valid. Nor even on m-w.com (which I believe is a better site).

One of my favorite books is Garner's Modern American Usage. Its a great book and is more than a dictionary - it is a reference and guide on how American English is used.

"Atomic" is a good example of a word we use in software development all the time that is somewhat of a "made up" word. In a development context something that is atomic either happens, or does not happen - it cannot be divided into separate operations. But, the common definition for this word doesn't take this usage into account.

Bah! Here is a better one.... "Grep" Not in the dictionary - but yet, a perfectly good word. I use it all the time