'crusader' originates from Middle English, specifically formed from the word 'crusade' (from Old French 'croisade'), where the root 'crois' / Latin 'crux' meant 'cross'.

'crusader' changed from Old French 'croisade' (and Medieval Latin 'cruciata', meaning 'marked with the cross') and eventually became the modern English word 'crusader' through Middle English formations.

Initially, it meant 'one who took part in a religious military expedition to recover the Holy Land', but over time it evolved to include the broader meaning 'someone who energetically campaigns for a cause'.