A retronym is a newer name for an existing thing that helps differentiate the original form from a more recent one. It is thus a word or phrase created to avoid confusion between older and newer types, whereas previously (before there were more than one type) no clarification was required.
Advances in technology are often responsible for the coinage of retronyms. For example, the term acoustic guitar was coined with the advent of electric guitars; analog watches were renamed to distinguish them from digital watches once the latter were invented; and "push bike" was created to distinguish from motorbikes and motorized bicycles; finally "feature phone" was also coined behind smartphones.
The global war of the early 20th Century from 1914 to 1918 was referred to at the time as the "Great War". However, after World War II (also known as the Second World War) erupted in 1939, the Great War was gradually more commonly referred to instead as World War I or the First World War.
The first bicycles with two wheels of equal size were called "safety bicycles" because they were easier to handle than the then-dominant style that had one large wheel and one small wheel, which then became known as an "ordinary" bicycle.
