Errors & Omissions: Oil and petrol don't usually mix – rather like these metaphors

Pouring oil on troubled waters is one of the most popular demonstration displays at the Museum of Ancient Metaphoric Curiosities, almost as popular with the kiddies as the daily demonstrations of battening down the hatches and changing horses in mid-stream.

A visit to the museum might be profitable for the writer of this sentence, from a comment piece published on Tuesday, speaking of Alistair Darling's memoirs and the damage they have done to Gordon Brown's reputation: "I suspect he is alert to the damage. He looked nervous in his interview with Andrew Marr on Sunday. At one point he said: 'If Gordon is watching this ...' The image of Brown watching his old friend pour oil on the wreckage of his reputation is enough to make anyone nervous."

Apparently, you can reduce the turbulence of water by pouring a film of oil on to the surface. It sounds unlikely to me, and why would anyone want to do it? But there you are; that is what the metaphor is all about. Pouring oil is meant to calm things down. What Alistair Darling is doing to Gordon Brown's reputation sounds more like pouring petrol on a fire. (Unfortunately, health and safety regulations have forced the museum authorities to suspend that once popular display.)

Struggling: Derek Watts writes in to draw attention to this, from a news story published on Monday: "It is the second year running that Cambridge University has taken the top spot. It wrestled first place from Harvard last year."

"Wrestle" should be "wrest", but the error, a common one, is perhaps forgivable. The two words are descended from different parts of the Old English verb wraestan, meaning to twist. But their meanings have diverged over the centuries, as these things will. Today "wrestle" means to strive to overcome an opponent by grappling, while "wrest" means to seize by force.

End of the line: Perhaps the time has come to declare "heir apparent", in its original meaning, a lost cause. Wednesday's front-page splash began thus: "James Murdoch's status as heir apparent to his father's News Corp empire was in the hands of 11 MPs last night."

"Heir apparent" is used here to signify the heir to some great dynastic inheritance, as opposed to a mere heir, who simply stands to inherit something more humble, such as a sum of money or your grandfather's watch.

That seems to be the common usage today. It is obliquely derived from the original use of the term in feudal legality. An heir apparent is one (usually an eldest son) who cannot be superseded by the birth of a nearer heir. One who can be so displaced is an heir presumptive. Not many people remember that.

Strange noises: "At times yesterday the only sound coming out of the Thatcher Room in the palace of Westminster was the thunk of the buck being passed between senior figures who once ran Rupert Murdoch's British newspaper empire."

So began a commentary published on Wednesday. Does a buck go "thunk"? That depends on what this buck is that everyone is always passing (until, of course, it stops). According to the Oxford Dictionary of Idioms, the buck is an object placed on a poker table as a reminder of whose turn it is to deal the hand. So, to pass the buck is to pass a responsibility to someone else. I suppose it is conceivable that it might be bulky enough to go "thunk".

However, the situation may not be quite as simple as that. In the poker-playing circles frequented by one of my sons, the marker that shows who is dealer is called not the buck but the button. Hence, "on the button"? Who knows?

Rock or a hard place: "Industry insiders sometimes joke that if Danish TV audiences were given a choice between a von Trier movie or the test card, almost all would watch the test card." That is from an article in last Saturday's magazine. "Between X or Y" seems to be more and more common. It should be either "a choice of X or Y" or a "a choice between X and Y".