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'. 

They wait you

Sounds sinister, that title, like a line from a classic ghost story. It's not - I said it, in the perfectly pleasant surroundings of Côte in Covent Garden, talking about the lunch we'd had that day in the London Review Bookshop.

This bookshop is a very nice bookshop with a small selection of linguistics books hidden at the bottom of a small set of shelves in the basement. But I wasn't there to peruse the books. It was lunchtime, I was having a break from seeing Ice Age things at the British Museum with my parents and we needed some lunch before going to see Pompeii and Herculaneum things. There's a very nice cafe in the bookshop, selling home-made sorts of food and a million types of tea. It's small though, and popular, so we had to wait for a table. The waitress suggested we wait in the bookshop and she'd come and get us when there was a free table.

I was telling my aunt about this when we met her later on, and I said:

They wait you in the bookshop.

Wait is not normally used this way, but I liked it so I let it stand. Normally, wait doesn't have an object - that is, (roughly) something acted on by the verb. Sleep doesn't have an object (I slept) but catch does (I caught a rabbit), and eat either can or can't (I've eaten or I've eaten six Jaffa cakes). Wait is like sleep (I  waited). What I said included an object: They wait you (we can ignore in the bookshop for now, because it's optional in the sentence).

Sometimes, we have verbs that change the number of objects they have (in this case from 0 to 1) because of some syntactic difference. This is different from eat, which either has a 'null' object meaning 'some unspecified kind of food' or just has two very closely related meanings.

Wait normally has a subject which is the person doing the waiting: if I say I waited, it's me who's done the waiting. With eat, that subject stays the same whether we add an object or not: I ate or I ate six Jaffa cakes, it's still me who ate something. But look at the sentence above: the subject is not the person who is waiting. When I said They wait you in the bookshop, it's not 'they' who are waiting, it's the object of the sentence, you (=us, in that case). So when I added the object, I also changed the role of the participants in the action.

What I meant by that utterance was, I suppose, They make you wait in the bookshop or They cause you to wait in the bookshop. I've turned it into what linguists, in an uncharacteristic show of naming things transparently, call a 'causative'. It's comparable to grow: I can say either I grew, and then it is me who became larger, or I can say I grew a plant or I grew the profits and then it is something else that I have caused to become larger.

It's also related to something called 'middle voice'. It's called that because it's in the middle between active and passive. If you think about a sentence like The cake cuts well, then the cake is grammatically the subject of an active verb, but the meaning is that the cake is the thing that is cut, and that's the meaning you'd get from a passive form: The cake has been cut. English doesn't do this loads, compared to some other languages, and that's not what's happening with wait above. It's just a similar phenomenon.