It’s perhaps no surprise that contemporary definitions of the word “terrorism” have largely narrowed somewhat, but one of the Oxford English Dictionary’s definitions of “terrorism” still represents the broader usage:
The instilling of fear or terror; intimidation, coercion, bullying.
The first use of the term is believed to have been around 1794 and was in reference not to to the use of terror as a tool to undermine governments, but to the use of terror by governments themselves. Only a few years later it was being used in reference to the British government of the time.