I've learnt a fun new word: 'retronym'. A retronym describes an item renamed because of the arrival of a newer version which renders its label outdated or no longer unique. So, 'World War One' is a retronym, because it wasn't called that until World War Two came along. As are 'acoustic guitar', 'black and white TV', 'Before Christ' and 'silent film'.
Here are some less obvious ones, which I enjoyed:
- Forward slash: before MS-DOS introduced the backslash ( \ ), what we now call the forward slash was known simply as 'a slash'
- George HW Bush: Bush Senior didn't use his initials publicly until his son Dubya became President
- Cold-water tap: it was just 'the tap' before the invention of the water heater
More retronyms here