The definition is self referential. You have to have the result to have the thing itself. This does not work. Trauma is trauma
Regardless of the reaction or interpretation of the person/persons experiencing the event, the event did happen. Everyone who expereinces the event directly or indirectly is impacted by the event, if in no other way than to have a new neuronal pathway with the memory. What people do with the event may vary, many times depending on the resiliency of the person and the environment.
As adverse childhood events are the greatest indicator of adult mental health issues, it is important to address the trauma immediately and not when the effects show up sometime later.
Shirley Haney commented
There have been some studies that suggest that addressing an event immediately afterward, for example by grief counselors sent in after an event, can actually create more. trauma. I am sorry to not site studies, this is just from my Abnormal Psychology textbook.
Darby Penney commented
I think it's important to note that trauma is the result of an external threat that overwhelms an individual's coping resources. A given violent or threatening event is not necessarily traumatizing to everyone who is impacted by it. One has only to look at combat veterans to see an example of this - not everyone who experiences combat is traumatized by it. I could give examples in my own life where I was definitely traumatized by some violent incidents, yet at other times in my life had the coping resources to come through a different violent incident with no lasting adverse effects.