My wife is a very patient woman. She puts up with a lot of my random musings. While fixing breakfast yesterday, I made a comment that something—I can’t remember what—was indescribable. That made me pause. “Doesn’t indescribable, in fact, describe the object?” I asked her. She assured me it didn’t, to which I said, “But it’s an object that cannot be described, so that is a description of the object, isn’t it?”
“Do you think I should change the water on these flowers?” she asked.
“Don’t you find that interesting?” After years of this dance, I already knew her answer to that question. I readily acknowledge I have a tendency to rail about the quirkiness of the English language—don’t get me started on why we have the letter “c” when “s” and “k” already cover all the work!
I tried to draw her back into the conversation. “So is that a tautology?”
“Isn’t it an oxymoron?” she asked, accepting the bait.
“I don’t think so,” I said. We then had a brief discussion about oxymorons and decided that it was not an oxymoron. We never did figure out what it should be called. My wife’s interest ran out long before we got there.
“I’m going to wrap some packages,” she said and retreated to somewhere I wasn’t.
Turns out that while tautology is a great word, it doesn’t describe a situation where the existence of a word actually invalidates itself (e.g., indescribable does in fact provide a description). I still don’t know what it’s called, and it’s going to drive me crazy. If anyone knows, please set my mind at ease and tell me what this is in a comment.
D. Thomas Minton 
The word you seek is “antinomy”. You can use this word to assert your superiority over your less evolved friends, and also apply it to your problem, which will then get much worse.
In order to understand what is meant by “indescribable” we can start with “describable”. Let us agree that a “description” of X must consist of a collection of true statements about X and no false statements . Consequently “X is indescribable” must mean that there are no true statements about X. Now consider the sentence:
The sentence “X is indescribable.” is a description of X.
Suppose this sentence is true. Since it concerns X, this implies that X is describable. The sentence then says that the false statement , “X is indescribable.”, is a description of X. Therefore, the sentence is false.
I think this means two things: (1) The sentence “X is indescribable.” is closely related to “This sentence is false”. (2) Sensible people don’t worry about these things.
Servant of Cthulhu
John, thanks for the new word, “antimony”. After consulting my handy online dictionary, I see it is the perfect word. My goal is is now to use it at least once today, if for no other reason than to assert my superiority. I love it when logic (even Cthulhuian logic) can be used to expose the idiosyncrasies (or should it be the inanities?) of the English language.