TOMORROW is the biggest day in the British sporting year. It is an event that brings in a crowd of 200,000 annually — a quarter of a million and more on a nice day. This makes it the third-biggest annual event in the world, after the Indianapolis 500 and the Indianapolis 500 practice day. It is the third day of the Badminton Horse Trials, when the cross-country is held.

That is not something people expect. People think of horses as a fringe pursuit, something to do with a few eccentrics. But horses are part of our lives in 21st-century Britain, part of the way we speak and part of the way we think. I have a right to be heard on this, even if I am only a humble hack.

Hack is a locution borrowed from the horsey world — and not the only one. We speak to each other as if horses were still part of our daily lives. Hack is shortened from Hackney, which was a horse that you could hire. Therefore it was not up to much else, like the car you hire at the airport. So a hack was a sorry drudge, a horse from which not too much was expected. It was used figuratively and came to mean a literary drudge, a penny-a-liner, a term used of journalists with amiable contempt, and by journalists of themselves with a kind of epic false modesty.

But the word has been reborn in the horsey life. A smart trainer at Newmarket will ride out on the Heath on his hack, which may be a sumptuous former racehorse. It has become a verb: riders hack out on their horses, riding for the straightforward pleasure of it. A hack is not the horse but an out-and-back journey on horseback. The word has moved from contempt to joy.

Horsey words and phrases gallop through the English language and we are quite unaware of it. Before you embark on an important project, you do the groundwork, yes? Before I ride my young horse, I also do a spot of groundwork, which is the opposite of ridden work. I stand on the ground, which is harder to fall off than a horse, and work the horse on a long line, preparing her for ridden work. She is a little tired and back in the rhythm of working with me. Before you ride a young horse for the first time, it is customary to do weeks of groundwork.

When there is a new recruit at work, you will generally get someone to put him through his paces. That is what you do when buying a horse or, for that matter, when doing any basic schooling or exercise of a horse. The paces you put a horse through are, of course, walk, trot and canter. You want to be sure that a horse is capable of performing all those paces well.

Let’s stick with this new recruit. You might find that he wants his own way all the time: that he is stubborn and wilful. In fact, you may conclude that he is rather headstrong. A headstrong horse is one who is, quite literally, strong in the head: that is to say he leans on the bit, pulls, refuses to listen to requests to slow down.

Perhaps the recruit is a bit flighty, impetuous. You want to keep him on a tight rein. This is a more knowingly horsey expression, of course, but I include it for the interesting fact that restricting a horse or a human being on a tight rein never produces the desired result. Both are more likely to relax and accept their situation on a loose rein — if they are given their heads, in fact.

If you spend a lot of time yanking on a horse’s reins, you are likely to put his back up. It is not a good idea to put anybody’s back up, especially not a horse. When a horse puts his back up, it is because he is tense and angry and resentful, and thinking about bucking you off. I once rode a very nice horse that was subsequently ridden by Ginny Elliott, the great rider and three-times Badminton winner, so I facetiously claimed I had “got his back down for you”.

I hope I am not putting your back up with this stuff. Perhaps you are already getting fed up. When a horse is fed up, it has just consumed a large meal and cannot be ridden. The term might also be used of a horse in mild discomfort after a meal, in which case he is probably fed up to the back teeth. Humans have two single rows of teeth: horses have front teeth for shearing grass and back teeth for chewing it, and a pronounced gap between them.

If you feed a horse well, you will find that he is full of beans. Beans — no longer much used — are a high-protein food, and a horse on such a diet will show dynamic and spirited behaviour. In fact, a horse who behaves extravagantly might be feeling his oats — a phrase these days used of human beings in a sexual context.

A human in good form is often said to be leaping about like a two-year-old. This doesn’t refer to a two-year-old child: two-year-old children don’t leap. They stagger about and fall over. It is two-year-old horses — daft, cheerful and full of life — that do the leaping.

When I suggested the idea of this column to the sports editor, he pulled up short. That’s what happens to a horse with a sudden lameness, such as a stone bruise. It doesn’t mean that you stop in a short distance, it means that you have a sudden and very noticeable alteration in stride length, indicating unmistakably that there is something amiss. It is the length of stride that is short, not the distance.

Still, perhaps he is a bit long in the tooth to accept a radical idea like this. Humans don’t get longer teeth when they get old, but horses do, or appear to: the angle at which the teeth are set in the mouth changes with long use; they slant forward and appear doubly longer.

It is clear, then, that the idea of horses and horsemanship remains fossilised in our language, and it is language that dictates the way we think and the way we see the world. Horses have helped to shape our minds and our understanding. No doubt that is why Badminton attracts huge crowds: we are making a pilgrimage into the forces that shaped us.

Well, I have reached the end of my journey through the horsey hinterland of the human mind. I think I have made it safely. I am like a horse that has completed his work, has relaxed and is no longer hot and covered in sweat. In fact, I am home and dry.