It’s the word of the decade. “A major signifier of our age.” “The invisible force that shapes our lives.”

But what is “trauma”? Although it occupies the cultural spotlight, its meaning has never been hazier. Can we bring it into focus?

“Trauma” derives from the ancient Greek for wound. According to the Oxford English Dictionary, this external bodily injury meaning dates back to 1684.

Late in the 19th century, “trauma” acquired a second meaning as psychological injury. In 1894, for example, the US philosopher and psychologist William James wrote of “permanent ‘psychic traumata’”, likening them to “thorns in the spirit”.

A third, figurative meaning emerged in the 1970s. “Trauma” now referred to suffering or adverse events in general. Just as “schizophrenia” and “hysteria” originated as clinical diagnoses and later picked up new, broader senses, trauma expanded and became a metaphor.

Everyone seems to be talking about trauma. Do we know more about it? Or has the meaning changed? In this five-part series, we explore the shifting definition of trauma, why talking about it doesn’t always help, and what else can work.

Trauma in psychology and psychiatry

In the mental health disciplines, the definition of trauma has followed a winding path. In 1952’s first edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM), it referred exclusively to physical injury.

No diagnosis corresponding to the psychological meaning of “trauma” appeared until 1980, when DSM-III introduced post-traumatic stress disorder (PTSD).

DSM-III listed an array of PTSD symptoms and a definition of the kind of traumatic events responsible for them. For a diagnosis to be made, the event would have to evoke significant distress in almost everyone and be “outside the range of usual human experience”.

Controversially, later editions of the DSM loosened this criterion. For example, events that were indirectly........

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