Even with ruler and compasses I couldn’t make sense of a remark I found on Twitter or X, as we all pleonastically call it. Someone had posted this observation: ‘One’s bank balance and number of children are orthogonal to social media usage.’ I knew the prefix ortho– meant ‘straight, perpendicular, right’. So orthogonal meant ‘right-angled’. But how could children be at right angles to social media usage?

I hadn’t cottoned on to the fashion for using orthogonal figuratively to mean ‘unrelated’, ‘irrelevant’. That is quite a stretch, for things at right angles are not unrelated. But there is no stopping orthogonal now, though the term seems unhelpful. It’s not even as though it were intended humorously, as happened to the learned term opisthognathous. Prognathous or jutting jaws are found in the popular idea of cavemen; an orthognathous profile has the brow and chin straight up and down; a receding chin is opisthognathous.

Peter Fleming (elder brother of Ian) wrote humorous fourth leaders for the Times. On 22 November 1937 he asked: ‘What hero of fiction has ever had a receding chin?’

Eight days later, P.G. Wodehouse replied. ‘Compared with Sir Roderick Glossop, Tuppy Glossop, old Pop Stoker, Mr Blumenfeld, and even Jeeves, Bertie is undoubtedly opisthognathous. But go to the Drones and observe him in the company of Freddie Widgeon, Catsmeat Potter-Pirbright, and particularly Augustus Fink-Nottle, and his chin will seem to stick out like the ram of a battleship.’

Wodehouse was aware of scientists in his day who saw evolution from the prognathous to the orthognathous reflected in racial characteristics. Perhaps Gussie Fink-Nottle subverted this eugenic science, just as Roderick Spode with his Black Shorts mocked the Mosleyite Black Shirts.