Sorry? Can you spell that, please?

If it hadn't been for my son, I would never last week have come across a word that it is impossible to spell.

Impossible to spell satisfactorily, that is.

Can you think of a word that cannot be spelt satisfactorily? Apart from Popocatepetl? And "millennium"? And all those other words which always look wrong no matter how you spell them? Like "ipecacuanha"? Seems unlikely, doesn't it?

I had never come across a word which I could not think of a spelling for. Before my son put me on the track.

Well, I already know of one word that is impossible to write down in an acceptable way, but it is an abbreviation, so not really a whole word.

It is the shortened form of "casual".

"Casual" is not quite the simple word it seems to be. For a start, as you must know, it has at least two functions. One is as a misprint for "causal". Whenever a sub-editor sees the word "causal", he changes it automatically to "casual", just as the word "Bermudian" tends to be changed (wrongly) to "Bermudan" and the word "discrete" tends to be altered to "discreet". Mark you, I shouldn't be risking annoying my sub-editors so early in a piece, and if you find any puzzling things later on in this column, you will know that it is merely a case of a sub-editor taking his revenge.

But "casual" can also refer to sex and violence and clothes, and in the context of clothes ("casual jacket", "casual wear") it is sometimes shortened in a joky sort of way to a word that sounds a bit like "cadge" or perhaps "cash", but is actually if anything "cazh". See what I mean?

There is no generally accepted way of writing that sound down, so that word is never written down.

Right. We now come to last week when my son took me to the cinema. He is nine years old and he wanted to see Mars Attacks. Mars Attacks is a new joky science fiction film by Tim Burton, which also happens to be a "12" certificate. I explained to my nine-year-old that nine-year-olds cannot attend "12" films, and that there is a very good set of reasons behind the grading of films. He agreed but still demanded to be taken, so I took him. Despite one awkward moment (when he whispered out loud at the cinema cash till: "Don't forget to pretend I'm 12, Dad!"), we got in without trouble and left without being depraved. It was a very funny and imaginative film and I am glad I saw it rather than Independence Day.

Right. We now come to a day or two later when there was an interview with film-maker Tim Burton on BBC radio, which I listened to with interest as a new convert to Burton's films, and somewhere during the interview, the questioner asked Tim Burton if it was true, as he had heard, that Burton sometimes did without a script and storyboard and got his actors to improvise on screen. "Sure," said Burton. "Many of my performers have an improv comedy background, and quite a few of the scenes in some films are not written down - they are actually improv'd."

This shook me. I am used to "impro" or "improv" being used as an abbreviation for improvisation, in a theatre or comedy context, but I have never heard either of them being used as a verb before. What's the point? There is a perfectly good verb "improvise" already, so why say that an actor can "improv" a scene? Even in jazz, where people improvise the whole time, they tend not to use the word - the commonest word in jazz parlance for "improvise" is not "improvise" but "busk". I have never heard the word "improv" or "impro" used by a jazz artist.

But there is Tim Burton saying that some of his scenes are improv'd, and I say this. The reason you should not use the word is that you cannot write it down. You could write that "some of the scenes are improved", but you should not, because that means something else, namely, that some of the scenes are made better. And to improv is not necessarily to improve.

So how do you write the past tense of this peculiar new verb to "improv"? Do you inaccurately write "improv'd", as I have tried? Do you write "improvved"? Do you ban the use of the word "improv" as a verb at all, just to avoid problems like that?

Or do you just say: "firhsgqo bdnsk kkkwo hgingo oooow doftoonn5e8f8gjjsl------^*d- <</p>

Sorry. Sub-editors at workn