'diehard' originates from English, specifically the phrase 'die hard,' where 'die' meant 'to cease living' and 'hard' meant 'with difficulty' or 'resisting.'

'diehard' changed from the phrase 'die hard' (used to describe someone who resists death or is slow to die) and was later reanalyzed as the adjective and noun 'diehard,' applied figuratively to people who stubbornly resist change.

Initially, it meant 'to resist dying or be hard to kill,' but over time it evolved into its current meaning of 'a person who stubbornly resists change or gives unwavering support.'