'unstained' originates from the prefix 'un-' meaning 'not' and the word 'stained' from Old French 'estainier', meaning 'to stain'.

'stained' changed from the Old French word 'estainier' and eventually became the modern English word 'stain'.

Initially, 'stain' meant 'to color or dye', but over time it evolved into its current meaning of 'to mark or discolor'.