'betrayer' originates from Middle English, specifically the word 'betrayen,' where 'be-' meant 'thoroughly' and 'trahere' meant 'to pull or drag.'

'betrayen' transformed into the modern English word 'betray,' and eventually 'betrayer' was derived from it.

Initially, it meant 'to thoroughly pull or drag someone into a trap,' but over time it evolved into its current meaning of 'to deceive or be disloyal to someone.'