Sometimes we don't realise how much the vocabulary of psychology has become part of everyday language. I was surprised to learn that the use of the term 'stress' to mean psychological tension, rather than just physical pressure, has only been with us since the mid-1930s and was popularised by the major wars of the 20th century.

And it turns out, the person who coined the new usage did it by accident, owing to a mistaken translation. Akin to 'distress', 'stress' meant 'a strain upon endurance', but it was also used in a more specialist way by engineers to denote the external pressures on a structure - the effects of 'stress' within the structure became known as 'strain'.

Then in 1935 the Czech-Candian physiologist Hans Selye began to promote 'stress' as a medical term, denoting the body's response to external pressures (he later admitted that, new to the English language, he had picked the wrong word; 'strain' was what he had meant).

Academic physiologists regarded the concept of stress as too vague to be scientifically useful, but Selye's determined self-promotion, coupled with the upheaval and distress brought by the [Second World] war to many millions of ordinary people, popularised the term.

By the time of Vietnam, 'stress' had become a well-established part of military medicine, thought to be a valuble tool in reducing 'wastage'. In the military context, it was an extension of the work done at the end of the First World War on the long-term effects of fear and other emotions on the human system...

'Stress', writes the historian Russell Viner, 'was pictured as a weapon, to be used in the waging of psychological warfare against the enemy, and Stress research as a sheild or vaccination against the contagious germ of fear.'