'insider' originates from the English word 'inside,' combined with the suffix '-er,' indicating a person associated with a particular activity or place.

'inside' transformed from the Old English word 'insidan,' and eventually became the modern English word 'inside,' which then formed 'insider.'

Initially, it meant 'a person within a particular place,' but over time it evolved into its current meaning of 'a person with special knowledge or influence within a group.'