Disappearing, and being disappeared

The verb disappear is normally what we call 'intransitive', which means that it has one participant: the person who disappears. Like this: 

The leftovers disappeared. 

If anything follows the word disappear, it's either some extra optional information, or it's a continuation of the discourse and the 'disappear' phrase is done: 

The leftovers disappeared overnight. 

The leftovers disappeared, which I'm very annoyed about because I was going to have them for lunch today. 

If we want to talk about more than one participant, like if we have both the thing that disappears and also someone who causes the disappearing to happen, we have to add in another word, make: 

The kitchen staff made the leftovers disappear. 

English being the flexible language that it is, you can find examples of 'transitive' disappear, which is when we just put the two participants of the action right there with the verb: 

VICE has disappeared the post from its website (from M-W)

But English also being the kind of language that doesn't like redundancy (this is all languages tbh), because we already have a way of doing this with make, the 'cause to disappear' meaning takes on a more specialist meaning than the other one, so that they are distinct in their function as well as their form. Content warning now for examples relating to war and dictatorships. Here's some more examples from Merriam-Webster: 

Her son was disappeared during Argentina's so-called Dirty War.

Under his repressive regime, tens of thousands of Chileans were 'disappeared', tortured and killed. 

It [Nineteen Eighty-Four] imagines a secretive regime that surveils its people and polices even their thoughts, disappearing anyone who rebels against the order. 

It has taken on this specialised meaning of the imprisonment or killing of political dissidents. 

Perhaps, if you're paying close attention, you might notice that only the last one actually has two participants mentioned: the 'secretive regime' and 'anyone who rebels'. The others only mention the person who disappeared. But here we have an exception that proves the rule, because these are passive sentences (He was disappeared vs The government disappeared him). You can only make a passive sentence with a transitive verb, because to do so you need to promote the object (the thing the verb happens to) to be the subject of the sentence: 

I (subject) ate the leftovers (object).

The leftovers were eaten. 

You can't do it with a sentence with only one participant to begin with, because then there's no object to promote. Or, if you prefer, you can, but by doing so you're adding in another understood participant: 

Not passive, one participant: The boat sank (perhaps with no particular cause). 

Passive: The boat was sunk (by someone in particular, though we aren't told who). 

While it is true to say that the political dissidents disappeared, it is more informative to say that they were disappeared, because it informs us of the involvement of a third party who deliberately caused this 'disappearance'. 

Antidisestablishmentarianism is a very long word

There's a really great post at Merriam-Webster about why the word antidisestablishmentarianism isn't in the dictionary. Basically, it's because it isn't a word in common usage. This raises interesting questions about the nature of lexicography, what 'in common usage' means, meta-linguistic mention vs. use, and compositionality of meaning.

The word clearly does have a meaning. Merriam-Webster say it's this:

opposition to depriving a legally established state church of its status

I thought it was something like the movement against the separation of church and state, but maybe that's the same thing - I'm not at all clear about what that actually means. But the point is that the meaning arises directly as a sum of its parts: it's compositional. Well, this isn't strictly true: there is some idiomatic meaning to do with the church and the law as well. But the length of it comes from attaching affixes with strictly compositional meanings. When you have compositionality, you can theoretically create longer and longer words, up to the limit of your cognitive capacity. I could add a morpheme and create antidisestablishmentarianismation, for instance. Some long words in quite common use aren't in the dictionary simply because they're made by standard suffixation processes, and that suffix is in the dictionary so you can work out the meaning for yourself.

So antidisestablishmentariansim is a real word, in the sense that people recognise it and can understand its meaning and it's made with proper word-formation processes. But for M-W, it's not a word in common usage. They have only three quotations for this word which use the meaning they give above, and dictionaries rely on written uses of words. This is why they can seem slow: words only get in when they've achieved plenty of use in print materials.

They do have plenty of quotations of the word with reference to it being a long word, however. It is in the OED, and their quotations refer to this:

1984   T. Augarde Oxf. Guide Word Games xxvi. 216   The longest words that most people know are antidisestablishmentarianism..and supercalifragilisticexpialidocious.

This is metalinguistic mention of the word, not an actual use of the word. We're stepping outside language and talking about the word itself, not using the word to say something. This is sort of difficult to get your head round because we have to use language to talk about language, a long-recognised philosophical problem in linguistics.

Interestingly, M-W say at the end of their piece that it might be considered a viable entry 'simply because it's a well-known word'. The meaning is not well-known, however, so it would be an entry whose definition read something like 'famous long word', and the definition as a secondary bit of information. That would be quite cool and very meta.

Irrelevant postscript: There's a really stupid joke that goes like this: 'Antidisestablishmentarianism is a very long word. How do you spell it?' and the answer is, of course, 'I, T'. I sometimes try that out on my students and some of them groan but a lot of them simply don't understand the joke. Maybe it's the way I tell 'em.